NWLI


Line plots across dimensions of each concept
Tables

Table of contents


us-gaap:StatementClassOfStock
us-gaap:CommonStockParOrStatedValuePerShare
us-gaap:StatementClassOfStock
us-gaap:CommonStockSharesIssued
us-gaap:StatementClassOfStock
us-gaap:CommonStockSharesOutstanding
us-gaap:StatementClassOfStock
us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding
us-gaap:StatementClassOfStock
us-gaap:EarningsPerShareBasic
us-gaap:StatementClassOfStock
us-gaap:EarningsPerShareDiluted

us-gaap:Revenues
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:RealizedInvestmentGainsLosses

us-gaap:InsuranceCommissionsAndFees

us-gaap:NetInvestmentIncome
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:GainLossOnInvestments

us-gaap:OtherIncome
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:PolicyholderBenefitsAndClaimsIncurredNet
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:InterestCreditedToPolicyholdersAccountBalances
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:ConsolidationItems
us-gaap:OperatingExpenses
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:InterestPaidNet

us-gaap:AllocatedShareBasedCompensationExpense

us-gaap:BenefitsLossesAndExpenses

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:IncomeTaxExpenseBenefit
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:IncomeTaxesPaidNet

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax
us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossNetOfTax

us-gaap:NetIncomeLoss
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents
us-gaap:StatementClassOfStock
us-gaap:StatementEquityComponents

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:Assets
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:Liabilities

us-gaap:LiabilitiesAndStockholdersEquity

us-gaap:StockholdersEquity
us-gaap:CumulativeEffectPeriodOfAdoption, us-gaap:StatementEquityComponents
us-gaap:StatementEquityComponents

us-gaap:EquitySecuritiesFvNi
nwli:PricingSource
nwli:PricingSource, us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:FairValueByMeasurementBasis

us-gaap:DeferredIncomeTaxLiabilitiesNet

us-gaap:StockholdersEquity
us-gaap:CumulativeEffectPeriodOfAdoption, us-gaap:StatementEquityComponents
us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital

us-gaap:RetainedEarningsAccumulatedDeficit

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetIncomeLoss
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents
us-gaap:StatementClassOfStock
us-gaap:StatementEquityComponents

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:Dividends
dei:LegalEntity
us-gaap:StatementClassOfStock

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents
us-gaap:StatementEquityComponents
nwli:AmortizationOfUnrealizedGainLossOfAvailableForSaleSecuritiesTransferredToHoldToMaturitySecurities

nwli:ChangeInNetUnrealizedGainLossOnInvestmentSecuritiesHavingCreditLossesRecognizedInConsolidatedStatementOfIncomeNetofTax
us-gaap:StatementEquityComponents
nwli:ChangeInShadowDeferredPolicy

nwli:DeferralAndAmortizationOfSalesInducementsNoncashOperatingActivity

nwli:DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

nwli:HeldToMaturitySecuritiesRealizedGainsOnDisposal

nwli:HeldToMaturitySecuritiesRealizedLossesOnDisposal

nwli:IncreaseDecreaseInDebtSecuritiesAvailableForSaleAndHeldtomaturityAllowanceforCreditLoss

nwli:IncreaseDecreaseInDeferredPolicyAcquisitionCostsSalesInducementCostsAndValueOfBusinessAcquired

nwli:InvestmentsPercentageOfGainsOnBondsDueToCallsOfSecurities

nwli:NoncashorPartNoncashAcquisitionContingentConsiderationLiability

nwli:OtherComprehensiveIncomeLossSecuritiesAdjustmentsAndOtherThanTemporaryImpairmentLossesPortionAttributableToParent

nwli:PaymentstoAcquireEquitySecuritiesFVNI

nwli:PremiumsEarnedAndPolicyCharges
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:ConsolidationItems
nwli:RealizedInvestmentGainsLossesNetOfTax
us-gaap:ConsolidationItems
nwli:RealizedInvestmentGainsLossesTax
us-gaap:AwardType
nwli:SharebasedCompensationArrangementbySharebasedPaymentAwardPerformanceFactorPercentageOfPredefinedMetricTarget
us-gaap:AwardType, us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange
nwli:SharebasedPaymentArrangementOptionExercisePriceRange

nwli:TraditionalLifePremium

us-gaap:AccretionAmortizationOfDiscountsAndPremiumsInvestments
us-gaap:BusinessAcquisition
us-gaap:BusinessAcquisitionsProFormaNetIncomeLoss
us-gaap:BusinessAcquisition
us-gaap:BusinessAcquisitionsProFormaRevenue

us-gaap:DebtSecuritiesAvailableForSaleRealizedGain

us-gaap:DebtSecuritiesAvailableForSaleRealizedLoss

us-gaap:DebtSecuritiesHeldToMaturityCreditLossExpenseReversal

us-gaap:DebtSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairment
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAmortizationOfGainsLosses
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanContributionsByEmployer
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanInterestCost
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost
us-gaap:RetirementPlanType
us-gaap:DefinedBenefitPlanServiceCost

us-gaap:DepreciationAmortizationAndAccretionNet
us-gaap:DerivativeInstrumentRisk, us-gaap:HedgingDesignation, us-gaap:IncomeStatementLocation
us-gaap:DerivativeGainLossOnDerivativeNet
us-gaap:HedgingDesignation

us-gaap:EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:EmbeddedDerivativeGainLossOnEmbeddedDerivativeNet

us-gaap:EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense

us-gaap:EquitySecuritiesFvNiGainLoss

us-gaap:FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
us-gaap:FairValueByAssetClass
us-gaap:FairValueByAssetClass, us-gaap:IncomeStatementLocation
us-gaap:IncomeStatementLocation

us-gaap:FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
us-gaap:FairValueByLiabilityClass
us-gaap:FairValueByLiabilityClass, us-gaap:IncomeStatementLocation
us-gaap:IncomeStatementLocation

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
us-gaap:FairValueByAssetClass

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
us-gaap:FairValueByAssetClass

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
us-gaap:FairValueByAssetClass

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
us-gaap:FairValueByLiabilityClass

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases
us-gaap:FairValueByLiabilityClass

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
us-gaap:FairValueByLiabilityClass

us-gaap:GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments
us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:GainsLossesOnSalesOfInvestmentRealEstate

us-gaap:ImpairmentOfInvestments

us-gaap:IncreaseDecreaseInAccruedIncomeTaxesPayable

us-gaap:IncreaseDecreaseInAccruedInvestmentIncomeReceivable

us-gaap:IncreaseDecreaseInDeferredIncomeTaxes

us-gaap:IncreaseDecreaseInFuturePolicyBenefitReserves

us-gaap:IncreaseDecreaseInOtherOperatingAssets

us-gaap:IncreaseDecreaseInOtherOperatingLiabilities

us-gaap:IncreaseDecreaseInOtherPolicyholderFunds

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax
us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax
us-gaap:StatementEquityComponents

us-gaap:OtherCostAndExpenseOperating
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OtherNoncashIncome
us-gaap:InvestmentType
us-gaap:OtherOperatingIncome

us-gaap:OtherThanTemporaryImpairmentLossDebtSecuritiesPortionRecognizedInEarnings
us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent
us-gaap:StatementEquityComponents
us-gaap:OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentHeldtomaturitySecurities

us-gaap:PaymentsForDerivativeInstrumentInvestingActivities

us-gaap:PaymentsForProceedsFromPolicyLoans

us-gaap:PaymentsToAcquireAvailableForSaleSecuritiesDebt

us-gaap:PaymentsToAcquireBusinessesNetOfCashAcquired

us-gaap:PaymentsToAcquireHeldToMaturitySecurities

us-gaap:PaymentsToAcquireMortgageNotesReceivable

us-gaap:PaymentsToAcquireOtherInvestments

us-gaap:PresentValueOfFutureInsuranceProfitsAmortizationExpense1

us-gaap:ProceedsFromAnnuitiesAndInvestmentCertificates

us-gaap:ProceedsFromDerivativeInstrumentInvestingActivities

us-gaap:ProceedsFromLinesOfCredit

us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities

us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities

us-gaap:ProceedsFromSaleAndCollectionOfMortgageNotesReceivable

us-gaap:ProceedsFromSaleAndMaturityOfOtherInvestments

us-gaap:ProceedsFromSaleOfAvailableForSaleSecuritiesDebt

us-gaap:ProceedsFromStockOptionsExercised

us-gaap:ProvisionForLoanAndLeaseLosses

us-gaap:RepaymentsOfAnnuitiesAndInvestmentCertificates

us-gaap:RepaymentsOfLinesOfCredit

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareBasedLiabilitiesPaid

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
us-gaap:Range
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
us-gaap:Range
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeitures
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
us-gaap:AwardType
us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
us-gaap:AwardType, us-gaap:Vesting
us-gaap:TitleOfIndividual, us-gaap:AwardType, us-gaap:Vesting

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1

us-gaap:UndistributedEarnings
us-gaap:StatementClassOfStock

us-gaap:UnrealizedGainLossOnDerivatives
us-gaap:StatementClassOfStock
us-gaap:WeightedAverageNumberDilutedSharesOutstandingAdjustment
us-gaap:StatementClassOfStock
dei:EntityCommonStockSharesOutstanding

nwli:DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses
nwli:CreditRating
us-gaap:ConsolidationItems
nwli:DeferredPolicyAcquisitionCostsSalesInducementsAndValueOfBusinessAcquired
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:FairValueByFairValueHierarchyLevel
nwli:FairValueInvestmentsPercentOfTotal
us-gaap:FairValueByMeasurementBasis
nwli:InterestInTrustFairValueDisclosure
us-gaap:FairValueByFairValueHierarchyLevel
nwli:LiabilityForDeferredAnnuityContractsFairValueDisclosure
us-gaap:FairValueByMeasurementBasis
us-gaap:FairValueByFairValueHierarchyLevel
nwli:LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContractsFairValueDisclosure
us-gaap:FairValueByMeasurementBasis

nwli:LiabilityForFuturePolicyBenefitsUniversalLifeAndAnnuityContracts
us-gaap:FairValueByFairValueHierarchyLevel
nwli:LoansGrossInsurancePolicyFairValueDisclosure
us-gaap:FairValueByMeasurementBasis
us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable
nwli:MortgageLoansOnRealEstateAllowanceForPossibleLossPercentage
us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable
nwli:MortgageLoansOnRealEstateByLoansToValueRatioPercentage
us-gaap:FairValueByFairValueHierarchyLevel
nwli:MortgageLoansOnRealEstateCommercialAndConsumerNetFairValueDisclosure
us-gaap:FairValueByMeasurementBasis
nwli:MortgageLoansByLoanToValueRatio, us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable
nwli:MortgageLoansOnRealEstatePercentageOfTotalPercentage
us-gaap:FairValueByFairValueHierarchyLevel
nwli:OtherAssetsBookValueAndFairValueDisclosure
us-gaap:FairValueByMeasurementBasis
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:ValuationTechnique
nwli:PolicyholderAccountBalancesFairValueDisclosure
us-gaap:Range, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique
nwli:PolicyholderAccountsBalancesMeasurementInput
us-gaap:FairValueByFairValueHierarchyLevel
nwli:RealEstateFairValueDisclosure
us-gaap:FairValueByMeasurementBasis
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:ValuationTechnique
nwli:ShareBasedCompensationFairValueDisclosure
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique
nwli:ShareBasedCompensationMeasurementInput
us-gaap:Range, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique

us-gaap:AccruedIncomeTaxes

us-gaap:AccruedInvestmentIncomeReceivable

us-gaap:AllowanceForLoanAndLeaseLossesRealEstate
us-gaap:CumulativeEffectPeriodOfAdoption
us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable

us-gaap:AssetsFairValueDisclosure
us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
us-gaap:FinancialInstrument

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
us-gaap:FinancialInstrument

us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis
us-gaap:FinancialInstrument

us-gaap:AvailableForSaleSecuritiesDebtSecurities
nwli:PricingSource
nwli:PricingSource, us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:BusinessAcquisition
us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:FairValueByMeasurementBasis
us-gaap:FinancialInstrument

us-gaap:BusinessCombinationContingentConsiderationLiability
us-gaap:BusinessAcquisition
us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:ValuationTechnique
us-gaap:FairValueByMeasurementBasis
us-gaap:Range, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique
us-gaap:BusinessCombinationContingentConsiderationLiabilityMeasurementInput
us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:CashAndCashEquivalentsFairValueDisclosure
us-gaap:FairValueByMeasurementBasis

us-gaap:CashCashEquivalentsAndShortTermInvestments
us-gaap:StatementClassOfStock
us-gaap:CommonStockValueOutstanding

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPosition
us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
us-gaap:FinancialInstrument
us-gaap:FinancialInstrument
us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions

us-gaap:DebtSecuritiesHeldToMaturityAllowanceForCreditLoss
nwli:CreditRating
us-gaap:CumulativeEffectPeriodOfAdoption
us-gaap:FinancialInstrument

us-gaap:DeferredPolicyAcquisitionCosts

us-gaap:DeferredSalesInducementsNet
us-gaap:Range, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique
us-gaap:DerivativeAssetMeasurementInput

us-gaap:DerivativeAssets
nwli:PricingSource
nwli:PricingSource, us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:BalanceSheetLocation, us-gaap:DerivativeInstrumentRisk, us-gaap:HedgingDesignation
us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:ValuationTechnique
us-gaap:FairValueByMeasurementBasis
us-gaap:HedgingDesignation

us-gaap:DerivativeLiabilities
us-gaap:BalanceSheetLocation, us-gaap:DerivativeInstrumentRisk, us-gaap:HedgingDesignation
us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:HedgingDesignation

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized

us-gaap:EquitySecuritiesFvNiCost

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
us-gaap:FairValueByAssetClass

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
us-gaap:FairValueByLiabilityClass
us-gaap:BusinessAcquisition
us-gaap:FiniteLivedIntangibleAssetsAccumulatedAmortization
us-gaap:BusinessAcquisition, us-gaap:FiniteLivedIntangibleAssetsByMajorClass
us-gaap:BusinessAcquisition
us-gaap:GoodwillGross

us-gaap:HeldToMaturitySecurities
nwli:CreditRating
us-gaap:BusinessAcquisition
us-gaap:FinancialInstrument

us-gaap:HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
us-gaap:FinancialInstrument

us-gaap:HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
us-gaap:FinancialInstrument

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
us-gaap:FinancialInstrument

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
us-gaap:FinancialInstrument

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
us-gaap:FinancialInstrument

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
us-gaap:FinancialInstrument

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
us-gaap:FinancialInstrument

us-gaap:HeldToMaturitySecuritiesFairValue
us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:FairValueByMeasurementBasis
us-gaap:FinancialInstrument

us-gaap:IncomeTaxReceivable

us-gaap:Investments

us-gaap:LiabilitiesFairValueDisclosure
us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:ConsolidationItems
us-gaap:LiabilityForFuturePolicyBenefits
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:LiabilityForFuturePolicyBenefitsLife

us-gaap:LoansInsurancePolicy
us-gaap:FairValueByFairValueHierarchyLevel
us-gaap:LoansReceivableFairValueDisclosure
us-gaap:FairValueByMeasurementBasis

us-gaap:MortgageLoansOnRealEstateCommercialAndConsumerNet
us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable
nwli:MortgageLoansByLoanToValueRatio, us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable
us-gaap:NotesReceivableGross
us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable

us-gaap:OtherAssets
us-gaap:OtherCommitments
us-gaap:OtherCommitment

us-gaap:OtherLiabilities

us-gaap:OtherLiabilitiesFairValueDisclosure
us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:OtherLongTermInvestments
us-gaap:InvestmentType

us-gaap:PolicyholderFunds
us-gaap:ConsolidationItems
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions
us-gaap:AwardType, us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions
us-gaap:AwardType, us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange
dei:LegalEntity
us-gaap:StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApproval

us-gaap:ValueOfBusinessAcquiredVOBA

Tables

  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
 us-gaap:CommonStockParOrStatedValuePerShare us-gaap:StatementClassOfStock us-gaap:CommonClassA▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁█▁▁█1e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-061e-081e-081e-06NANANA
 us-gaap:CommonStockParOrStatedValuePerShare us-gaap:StatementClassOfStock us-gaap:CommonClassB▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁█▁▁█1e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-081e-061e-081e-081e-06NANANA
 us-gaap:CommonStockSharesIssued us-gaap:StatementClassOfStock us-gaap:CommonClassA▁▁▁▁▁▁▁████████████████3.436023.436023.436023.436023.436023.436023.436023.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.436166NANANA
 us-gaap:CommonStockSharesOutstanding us-gaap:StatementClassOfStock us-gaap:CommonClassA▁▁▁▁▁▁▁████████████████3.436023.436023.436023.436023.436023.436023.436023.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.4361663.436166NANANA
 us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding us-gaap:StatementClassOfStock us-gaap:CommonClassA▄▄3.4363.436NA3.4363.4363.436NA3.4363.4363.436NA3.4363.4363.44NA3.4363.4363.437NA3.4373.4373.438NA3.438NANA
 us-gaap:EarningsPerShareBasic us-gaap:StatementClassOfStock us-gaap:CommonClassA█▁▇▄▆▇▄▆▆▅▇▄▅▅▅▆▅▄▆▄▅▄▅▅▅▄13.69-0.5810.675.659.5311.376.1610.089.187.611.196.177.216.666.689.547.434.889.054.598.166.037.958.058.265.61
 us-gaap:EarningsPerShareBasic us-gaap:StatementClassOfStock us-gaap:CommonClassB█▁▇▄▆▇▄▆▆▅▇▄▅▅▅▆▅▄▆▄▅▄▅▅▅▄6.85-0.295.342.834.765.683.085.044.593.85.63.083.63.333.344.773.722.444.522.294.083.023.984.034.132.8
 us-gaap:EarningsPerShareDiluted us-gaap:StatementClassOfStock us-gaap:CommonClassA█▁▇▄▆▇▄▆▆▅▇▄▅▅▅▆▅▄▆▄▅▄▅▅▅▄13.69-0.5810.675.659.5311.376.1610.089.187.611.196.177.216.656.679.547.434.889.044.598.166.037.948.058.255.61
 us-gaap:EarningsPerShareDiluted us-gaap:StatementClassOfStock us-gaap:CommonClassB█▁▇▄▆▇▄▆▆▅▇▄▅▅▅▆▅▄▆▄▅▄▅▅▅▄6.85-0.295.342.834.765.683.085.044.593.85.63.083.63.333.344.773.722.444.522.294.083.023.984.034.132.8
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
us-gaap:Revenues ▇▁█▅▆▇▁▇▆▃█▇▆▇▆▆▅▅▆▃▅▅▆▅▇▅216.01552.488235.428173.166192.685217.90942.486225.435174.658109.018247.815203.99198.226224.417184.485181.847167.094148.942180.583106.104155.218147.89184.315159.62206.841158.003
us-gaap:RealizedInvestmentGainsLosses ▅▅▄▁▁▆▄▄▄▂▆▄█▄▄▇▄▄▃▂▆▃▇▄3.1253.4852.539-0.502-0.4254.6292.8412.2752.6960.6113.8572.0746.2472.5852.4815.4262.7822.3811.160.8134.2580.9784.8582.169NANA
us-gaap:InsuranceCommissionsAndFees ▃▁▃▄▃▄▄▄▆▄▃▆▇▇▆▆▇█▇▅▄▃▄▂36.86935.30637.01837.8436.9137.95338.45238.28739.94538.5237.63940.26840.69741.36439.65640.33341.44842.0140.77539.17538.34537.31337.77236.602NANA
us-gaap:NetInvestmentIncome ▆▁▇▅▆▇▁▇▆▄█▇▆▇▆▆▅▅▆▃▅▅▆▅145.694-13.478167.281108.456128.424151.331-9.023175.553121.80260.745193.64151.691142.612171.742131.942126.981113.25195.5120.72356.209102.25999.923130.834110.966NANA
us-gaap:GainLossOnInvestments ▅▅▄▁▁▆▄▄▄▂▆▄█▄▄▇▄▄▃▂▆▃▆3.1253.4852.539-0.502-0.4254.6292.8412.2752.6960.6113.8582.0736.2472.5852.4815.4262.7822.3811.160.8134.2580.9784.38NANANA
us-gaap:OtherIncome ▄▁▁▁▂▃▂▂▃▂▄▂▂▂▂▂▂▂█▂▂▃▃▃7.5863.6533.8343.2733.9666.4135.2075.1115.2874.9977.3564.6724.5374.5054.8514.4764.6964.87812.5765.0675.1945.3295.2795.377NANA
us-gaap:PolicyholderBenefitsAndClaimsIncurredNet ▇▇▇█▇▆▄▁▃▄▂▄▃▄▃▃▃▃▃▃▃▄▃▃33.43133.63435.57839.91833.65728.18920.695.74417.46121.40112.85921.01517.85419.75716.95817.4315.5415.60117.88514.18116.1219.26613.37313.163NANA
us-gaap:InterestCreditedToPolicyholdersAccountBalances ▅▂▆▅▅▆▁█▅▃█▇▆▇▅▅▅▅▅▃▅▅▆▅61.772-28.02694.8359.44560.13980.916-47.261124.14560.99-1.818137.157107.79982.17109.89368.79867.77662.79949.01762.17216.25949.43149.03973.68359.211NANA
 us-gaap:OperatingExpenses us-gaap:ConsolidationItems us-gaap:OperatingSegments▇▂█▆▆▇▁▇▆▃█▇▇█▆▆▅▅▆▄▅▅166.94653.818197.161153.283159.078176.73920.113189.316141.62682.015206.878181.451170.557199.974160.004146.212139.835130.849148.18789.599124.869126.222NA130.394NANA
 us-gaap:OperatingExpenses us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nwli:AcquiredBusinesses█▇▇▇█▁25.11323.91923.5724.27624.84616.255NA0.00.00.0NANANANANANANANANANANANANANANANA
 us-gaap:OperatingExpenses us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nwli:Annuities▅▂▆▅▅▅▁▆▅▃██▆▇▆▅▅▅▅▃▄▅80.2233.26297.30877.76380.97291.01517.9498.41383.89446.264132.546133.16104.541123.8597.51689.25391.90583.81284.37454.44275.29978.74NA81.092NANA
 us-gaap:OperatingExpenses us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nwli:DomesticLifeInsurance▇▁█▆▆▇▁█▆▄▇▆▆▇▆▅▅▄▅▄▅▅32.365-8.7638.34724.73725.22733.22-6.21136.50922.919.86830.02325.26624.56728.60822.07617.31618.43313.30218.0968.46114.94915.897NA13.015NANA
 us-gaap:OperatingExpenses us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,nwli:InternationalLifeInsurance▅▁▆▄▄▅▁█▅▄▆▃▆▇▆▆▄▅▆▄▅▄25.4714.44634.86224.12723.77928.9212.27648.17227.61419.84637.94217.09834.49440.77533.48933.90322.62727.46635.91320.27427.82125.152NA29.603NANA
 us-gaap:OperatingExpenses us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,us-gaap:AllOtherSegments▃▁▃▂▄▆▅▅▆▅▅▅▆▆▆▅▆▅█▅▆▅3.7770.9513.0742.384.2547.3286.1086.2227.2086.0376.3675.9276.9556.7416.9235.746.876.2699.8046.4226.86.433NA6.684NANA
us-gaap:InterestPaidNet ▁▁▁█▁▁▁▁▁▁▁0.0190.0190.0190.2230.010.0190.010.010.010.010.01NANANANANANANANANANANANANANANA
us-gaap:AllocatedShareBasedCompensationExpense ▅▁▅▅▄▃▃▅▄▄▄▄▆▄█▅▃▃▅▃▄▄▅▄2.4-6.32.31.50.1-1.5-1.01.71.3-0.5-0.61.33.60.89.01.7-1.3-1.51.7-1.0-0.8-0.81.90.0NANA
us-gaap:BenefitsLossesAndExpenses ▆▂▇▆▆▆▁▇▅▃█▆▆▇▆▅▅▅▅▃▄▅▆▅155.45755.467187.999148.174150.541167.31819.629180.701134.31575.445211.382170.132159.425188.954146.456133.196126.708123.145133.25880.98112.423116.467143.043116.292NANA
us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest █▁▇▄▆▇▄▆▆▅▅▅▆▅▆▇▆▄▇▄▆▅▆▆60.558-2.97947.42924.99242.14450.59122.85744.73440.34333.57336.43333.85838.80135.46338.02948.65140.38625.79747.32625.12442.79531.42341.27343.328NANA
us-gaap:IncomeTaxExpenseBenefit ▇▂▆▄▅▆▃▆▅▅▁▇▇▇███▅█▆▇▆▇█12.145-0.9179.6965.0038.44810.3931.0819.0937.8776.698-3.15412.04513.31811.92514.41714.91514.18.53815.3358.90313.93710.09713.1614.862NANA
us-gaap:IncomeTaxesPaidNet ▂▂▃▄▅▂▂▂▄▃▄▃█▃▅▄▂▁0.0010.0012.39510.60824.1490.001-0.4810.00311.3978.28312.1457.59847.2665.4423.21115.0320.0-10.0NANANANANANANANA
us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax NA-0.0390.0050.052-0.0860.5530.1270.020.0391.168-0.0040.166-0.086-0.085-0.0830.022-0.2030.0990.0980.054-0.0530.0410.08-0.003NANA
us-gaap:OtherComprehensiveIncomeLossNetOfTax NA-80.8580.13116.51538.55241.925-2.7430.469-13.79-30.818-8.8220.4895.6713.86-35.8291.17420.86624.011-19.497-7.584-23.3829.006-5.931-8.953NANA
us-gaap:NetIncomeLoss █▁▇▄▆▇▄▆▆▅▇▄▅▅▅▆▅▄▆▄▅▄▅▅▅▄48.413-2.06237.73319.98933.69640.19821.77635.64132.46626.87539.58721.81325.48323.53823.61233.73626.28617.25931.99116.22128.85821.32628.11328.46629.18319.826
us-gaap:ComprehensiveIncomeNetOfTax █▁▅▅▆▆▄▅▄▃▄▄▄▄▃▅▅▅▄▄▄▄▄▄152.252-82.9237.86436.50472.24882.12319.03336.1118.676-3.94330.76522.30231.15427.398-12.21734.9147.15241.2712.4948.6375.47630.33222.18219.513NANA
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
us-gaap:Assets ▇▆████▄▅▅▅▆▅▅▅▄▄▄▃▃▂▂▂▁▁12391.73112284.42212553.44712559.59412612.9512648.87611931.69112091.8412085.81912126.31812225.09412138.29112021.26212032.75611894.98111880.60411801.21711683.69511612.57611546.14511515.29411462.00311351.89211259.076NANA
us-gaap:Liabilities ▄▄▆▆▇█▂▄▄▄▅▅▄▄▃▃▃▂▂▁10209.00110253.94410425.20410467.94210557.80210665.97610030.91410208.82310238.91210298.08710392.9210335.60910240.88210283.5310173.15310145.28610100.80810030.43910000.599945.38NANA9795.572NANANA
us-gaap:LiabilitiesAndStockholdersEquity ▆▆▇▇██▃▄▄▅▅▅▄▄▃▃▃▂▁▁12391.73112284.42212553.44712559.59412612.9512648.87611931.69112091.8412085.81912126.31812225.09412138.29112021.26212032.75611894.98111880.60411801.21711683.69511612.57611546.145NANA11351.892NANANA
us-gaap:StockholdersEquity █▆▇▇▇▆▅▅▄▄▄▄▄▃▃▃▃▂▂▂▂▂▁▁2182.732030.4782128.2432091.6522055.1481982.91900.7771883.0171846.9071828.2311832.1741802.6821780.381749.2261721.8281735.3181700.4091653.2561611.9861600.7651592.1281586.6521556.321534.138NANA
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
us-gaap:EquitySecuritiesFvNi ▃▁█▄▄▄▂▄▃17.91815.98423.59419.46219.32419.19617.49119.66118.637NA18.478NANANANANANANANANANANANANANANA
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
us-gaap:DeferredIncomeTaxLiabilitiesNet █▁▄55.42830.43839.907NANANA39.384NANANANANANANANANANANANANANANANANANANA
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
us-gaap:StockholdersEquity █▆▇▇▇▆▅▅▄▄▄▄▄▃▃▃▃▂▂▂▂▂▁▁2182.732030.4782128.2432091.6522055.1481982.91900.7771883.0171846.9071828.2311832.1741802.6821780.381749.2261721.8281735.3181700.4091653.2561611.9861600.7651592.1281586.6521556.321534.138NANA
us-gaap:AdditionalPaidInCapital ███████████████████▁41.71641.71641.71641.71641.71641.71641.71641.71641.71641.71641.71641.71641.71641.71641.71641.71641.71641.71641.71638.116NANA38.116NANANA
us-gaap:RetainedEarningsAccumulatedDeficit █▇█▇▇▆▆▆▅▅▄▄▃▃▃▂▂▂▁▁2057.8892009.4762026.3831989.9231969.9341936.2381896.041875.5371839.8961807.431776.1411740.3581718.5451693.0621669.5241647.1851613.451587.1641569.9051539.187NANA1472.782NANANA
us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax █▂▇▇▆▃▁▁▁▂▄▄▄▄▄▆▆▅▃▄83.089-20.7560.10859.97743.4624.91-37.015-34.272-34.741-20.95114.28120.57220.08314.41210.55246.38145.20724.340.32919.826NANA41.786NANANA
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
us-gaap:NetCashProvidedByUsedInOperatingActivities ██▆▅▅▆█▅▅▅▆▄▁▇▄▃▆█▇▆▄▆▆102.918105.66187.02878.11474.48389.404104.52176.94272.28772.87382.73662.64638.31692.43262.91760.76282.157103.30798.96889.0867.40990.76783.53NANANA
us-gaap:NetCashProvidedByUsedInInvestingActivities ███▇█▆▆▇▇▄▅▆▇▆▂▆▃▅▄▄▄▁▆136.03137.768126.2994.812130.17926.5937.37772.41759.113-110.978-11.2521.3550.716-6.019-184.05132.281-130.114-27.681-75.297-79.325-98.275-271.5129.782NANANA
us-gaap:NetCashProvidedByUsedInFinancingActivities ▂▁▂▂▁▁▂▂▃▃▆▆▄▅▆▆▇▅▆▇█▆█-140.344-144.689-131.308-142.285-155.687-156.737-135.464-120.522-87.854-98.074-24.414-22.759-67.319-50.043-4.781-9.7680.678-40.216-4.1934.83831.525-25.27242.562NANANA
us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect ▁█98.48898.69NANA48.866-40.04NANANANANANANANANANANANANANANANANANANANA
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
us-gaap:NetCashProvidedByUsedInOperatingActivities ██▆▅▅▆█▅▅▅▆▄▁▇▄▃▆█▇▆▄▆▆102.918105.66187.02878.11474.48389.404104.52176.94272.28772.87382.73662.64638.31692.43262.91760.76282.157103.30798.96889.0867.40990.76783.53NANANA
us-gaap:NetIncomeLoss █▁▇▄▆▇▄▆▆▅▇▄▅▅▅▆▅▄▆▄▅▄▅▅▅▄48.413-2.06237.73319.98933.69640.19821.77635.64132.46626.87539.58721.81325.48323.53823.61233.73626.28617.25931.99116.22128.85821.32628.11328.46629.18319.826
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
us-gaap:NetCashProvidedByUsedInInvestingActivities ███▇█▆▆▇▇▄▅▆▇▆▂▆▃▅▄▄▄▁▆136.03137.768126.2994.812130.17926.5937.37772.41759.113-110.978-11.2521.3550.716-6.019-184.05132.281-130.114-27.681-75.297-79.325-98.275-271.5129.782NANANA
us-gaap:PaymentsToAcquirePropertyPlantAndEquipment ▁▁▁▁▁▁▁▁▁▁▂▁▁▁█▁▁▁0.2170.0580.3471.4950.9250.0770.0680.0820.4352.5537.4191.4640.1890.04450.2140.00.00.0NANANANANANANANA
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
us-gaap:NetCashProvidedByUsedInFinancingActivities ▂▁▂▂▁▁▂▂▃▃▆▆▄▅▆▆▇▅▆▇█▆█-140.344-144.689-131.308-142.285-155.687-156.737-135.464-120.522-87.854-98.074-24.414-22.759-67.319-50.043-4.781-9.7680.678-40.216-4.1934.83831.525-25.27242.562NANANA
us-gaap:Dividends ▄▄0.00.0NANA0.00.0NANA-3.03.0NA4.04.0NANANANANANANANANANANANANA
 us-gaap:Dividends dei:LegalEntity nwli:NISFinancialServicesIncNA0.9NANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:Dividends us-gaap:StatementClassOfStock us-gaap:CommonClassA▁▁█▁▁▁█▁▁▁█▁▁▁█▁▁▁█▁▁▁▁█0.00.01.2370.00.00.01.2370.00.00.01.2370.00.00.01.2370.00.00.01.2370.00.00.00.0011.236NANA
 us-gaap:Dividends us-gaap:StatementClassOfStock us-gaap:CommonClassB▁▁█▁▁▁█▁▁▁█▁▁▁█▁▁▁█▁▁▁▁█0.00.00.0360.00.00.00.0360.00.00.00.0360.00.00.00.0360.00.00.00.0360.00.00.00.00.036NANA
  2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31

None

us-gaap:CommonStockParOrStatedValuePerShare us-gaap:StatementClassOfStock

us-gaap:CommonStockParOrStatedValuePerShare

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312008-06-202004-06-25
Value0.010.010.010.010.010.010.010.010.010.010.010.010.010.010.010.010.010.010.011.00.010.011.01.01.0
Percentage of CommonStockParOrStatedValuePerShare100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommonClassB


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value0.010.010.010.010.010.010.010.010.010.010.010.010.010.010.010.010.010.010.011.00.010.011.0
Percentage of CommonStockParOrStatedValuePerShare100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

None

us-gaap:CommonStockSharesIssued us-gaap:StatementClassOfStock

us-gaap:CommonStockSharesIssued

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value3436000.03436000.03436000.03436000.03436000.03436000.03436000.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.0
Percentage of CommonStockSharesIssued100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

None

us-gaap:CommonStockSharesOutstanding us-gaap:StatementClassOfStock

us-gaap:CommonStockSharesOutstanding

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value3436000.03436000.03436000.03436000.03436000.03436000.03436000.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.0
Percentage of CommonStockSharesOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

None

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding us-gaap:StatementClassOfStock

us-gaap:WeightedAverageNumberOfDilutedSharesOutstanding

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-30
Value3436000.03436000.03436000.03436000.03436000.03436000.03436000.03436000.03436000.03436000.03440000.03436000.03436000.03437000.03437000.03437000.03438000.03438000.0
Percentage of WeightedAverageNumberOfDilutedSharesOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

None

us-gaap:EarningsPerShareBasic us-gaap:StatementClassOfStock

us-gaap:EarningsPerShareBasic

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value13.69-0.5810.675.659.5311.376.1610.089.187.611.196.177.216.666.689.547.434.889.054.598.166.037.958.058.265.61
Percentage of EarningsPerShareBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommonClassB


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value6.85-0.295.342.834.765.683.085.044.593.85.63.083.63.333.344.773.722.444.522.294.083.023.984.034.132.8
Percentage of EarningsPerShareBasic50.050.050.050.149.950.050.050.050.050.050.049.949.950.050.050.050.150.049.949.950.050.150.150.150.049.9

None

us-gaap:EarningsPerShareDiluted us-gaap:StatementClassOfStock

us-gaap:EarningsPerShareDiluted

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value13.69-0.5810.675.659.5311.376.1610.089.187.611.196.177.216.656.679.547.434.889.044.598.166.037.948.058.255.61
Percentage of EarningsPerShareDiluted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommonClassB


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value6.85-0.295.342.834.765.683.085.044.593.85.63.083.63.333.344.773.722.444.522.294.083.023.984.034.132.8
Percentage of EarningsPerShareDiluted50.050.050.050.149.950.050.050.050.050.050.049.949.950.150.150.050.150.050.049.950.050.150.150.150.149.9

None

us-gaap:Revenues

us-gaap:Revenues


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value2165223517319221742225174109247203198224184181167148180106155147184159206158
Percentage of Revenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Revenues us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value2124923217319321339223171108243201191221182176164146179105150146179157
Percentage of Revenues98.693.498.9100.3100.297.993.399.098.599.498.499.096.898.898.797.098.398.499.499.297.399.397.498.6
Percentage of Revenues98.693.498.9100.3100.297.993.399.098.599.498.499.096.898.898.797.098.398.499.499.297.399.397.498.6
Percentage of Revenues us-gaap:OperatingSegments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Revenues us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value2828282828190.00.00.0
Percentage of Revenues13.354.912.316.614.98.80.00.00.0
Percentage of Revenues13.354.912.316.614.98.80.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:AcquiredBusinesses100.0100.0100.0100.0100.0100.00.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value10215113839510817129945814811911113110610292839755858410395
Percentage of Revenues47.429.148.348.149.649.641.957.354.053.960.058.656.358.757.556.655.556.053.852.355.256.956.360.1
Percentage of Revenues47.429.148.348.149.649.641.957.354.053.960.058.656.358.757.556.655.556.053.852.355.256.956.360.1
Percentage of Revenues us-gaap:OperatingSegments nwli:Annuities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value33-8.12639242534-6.4413623103127242821201813181015131713
Percentage of Revenues15.5-15.516.714.013.315.8-15.216.413.69.412.713.412.212.711.711.410.99.310.09.810.39.29.48.6
Percentage of Revenues15.5-15.516.714.013.315.8-15.216.413.69.412.713.412.212.711.711.410.99.310.09.810.39.29.48.6
Percentage of Revenues us-gaap:OperatingSegments nwli:DomesticLifeInsurance100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value341341313340174638294946435042434239443038394637
Percentage of Revenues15.826.517.618.517.218.440.120.721.827.419.822.622.222.323.224.125.226.624.628.524.626.425.323.4
Percentage of Revenues15.826.517.618.517.218.440.120.721.827.419.822.622.222.323.224.125.226.624.628.524.626.425.323.4
Percentage of Revenues us-gaap:OperatingSegments nwli:InternationalLifeInsurance100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value14-0.8849.5545.27210111110159.516149.0811211118.86119.639199.19511101110
Percentage of Revenues6.5-1.74.13.05.35.326.44.69.28.75.94.56.25.16.24.96.76.511.08.77.26.86.46.5
Percentage of Revenues6.5-1.74.13.05.35.326.44.69.28.75.94.56.25.16.24.96.76.511.08.77.26.86.46.5
Percentage of Revenues us-gaap:OperatingSegments us-gaap:AllOtherSegments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

None

us-gaap:RealizedInvestmentGainsLosses

us-gaap:RealizedInvestmentGainsLosses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value3.1253.4852.539-0.502-0.4254.6292.8412.2752.6960.6113.8572.0746.2472.5852.4815.4262.7822.3811.160.8134.2580.9784.8582.169
Percentage of RealizedInvestmentGainsLosses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues1.46.61.1-0.3-0.22.16.71.01.50.61.61.03.21.21.33.01.71.60.60.82.70.72.61.4

None

us-gaap:InsuranceCommissionsAndFees

us-gaap:InsuranceCommissionsAndFees


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value363537373637383839383740404139404142403938373736
Percentage of InsuranceCommissionsAndFees100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues17.167.315.721.919.217.490.517.022.935.315.219.720.518.421.522.224.828.222.636.924.725.220.522.9

None

us-gaap:NetInvestmentIncome

us-gaap:NetInvestmentIncome


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value145-13.478167108128151-9.02317512160193151142171131126113951205610299130110
Percentage of NetInvestmentIncome100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues67.4-25.771.162.666.669.4-21.277.969.755.778.174.471.976.571.569.867.864.166.953.065.967.671.069.5

us-gaap:NetInvestmentIncome us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value145-13.478167108128151-9.02317512160193151142171131126113951205610299130110
Percentage of NetInvestmentIncome100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues67.4-25.771.162.666.669.4-21.277.969.755.778.174.471.976.571.569.867.864.166.953.065.967.671.069.5
Percentage of Revenues us-gaap:OperatingSegments68.4-27.571.862.566.571.0-22.878.770.856.079.475.174.377.472.572.068.965.267.353.467.768.072.970.5

us-gaap:NetInvestmentIncome us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value6.5496.3016.316.36.0073.9760.00.00.0
Percentage of NetInvestmentIncome4.5-46.83.85.84.72.60.00.00.0
Percentage of Revenues3.012.02.73.63.11.80.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:AcquiredBusinesses22.821.921.821.920.920.70.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value97101097889103121238653144114105126101978677914979799890
Percentage of NetInvestmentIncome67.0-78.965.571.969.768.2-134.570.471.488.174.775.274.073.676.676.776.481.376.288.177.879.374.981.9
Percentage of Revenues45.220.346.645.046.547.328.654.849.849.158.455.953.256.354.853.651.852.150.946.751.253.653.256.9
Percentage of Revenues us-gaap:OperatingSegments nwli:Annuities95.469.696.493.693.895.568.295.792.291.297.295.594.596.095.494.693.393.194.789.292.894.294.594.6

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value21-19.38326121423-17.55226130.6632117151911129.5846.1339.9072.0958.0057.165106.859
Percentage of NetInvestmentIncome14.7143.815.711.911.715.5194.515.311.11.111.311.510.511.48.99.78.56.48.23.77.87.28.16.2
Percentage of Revenues9.9-36.911.27.47.810.8-41.311.97.80.68.88.57.68.76.36.85.74.15.52.05.24.85.84.3
Percentage of Revenues us-gaap:OperatingSegments nwli:DomesticLifeInsurance64.1238.566.953.058.368.4272.572.857.36.569.563.762.368.953.959.152.544.455.020.250.252.461.250.0

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value11-9.0166.8729.27614-9.70219101.971191514181212106.847110.4488.7858.614158.273
Percentage of NetInvestmentIncome7.766.810.16.37.29.3107.511.28.73.210.210.410.010.89.210.19.47.29.60.88.68.612.07.5
Percentage of Revenues5.2-17.17.24.04.86.4-22.88.86.11.88.07.77.28.36.67.06.34.66.40.45.75.88.55.2
Percentage of Revenues us-gaap:OperatingSegments nwli:InternationalLifeInsurance32.6-64.740.721.528.035.0-56.942.427.96.640.334.132.437.128.329.125.217.326.01.523.022.133.522.1

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value8.851-2.0288.2094.3998.5746.6856.0915.385104.5687.2794.4727.8647.0997.0134.546.5184.8817.3284.1485.964.9086.5014.999
Percentage of NetInvestmentIncome6.115.04.94.16.74.4-67.53.18.87.53.82.95.54.15.33.65.85.16.17.45.84.95.04.5
Percentage of Revenues4.1-3.93.52.54.43.114.32.46.14.22.92.24.03.23.82.53.93.34.13.93.83.33.53.1
Percentage of Revenues us-gaap:OperatingSegments us-gaap:AllOtherSegments62.6229.485.983.484.657.754.351.467.148.049.949.263.761.561.551.257.950.636.845.153.448.555.548.5

None

us-gaap:GainLossOnInvestments

us-gaap:GainLossOnInvestments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value3.1253.4852.539-0.502-0.4254.6292.8412.2752.6960.6113.8582.0736.2472.5852.4815.4262.7822.3811.160.8134.2580.9784.38
Percentage of GainLossOnInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues1.46.61.1-0.3-0.22.16.71.01.50.61.61.03.21.21.33.01.71.60.60.82.70.72.4

None

us-gaap:OtherIncome

us-gaap:OtherIncome


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value7.5863.6533.8343.2733.9666.4135.2075.1115.2874.9977.3564.6724.5374.5054.8514.4764.6964.878125.0675.1945.3295.2795.377
Percentage of OtherIncome100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues3.57.01.61.92.12.912.32.33.04.63.02.32.32.02.62.52.83.37.04.83.33.62.93.4

us-gaap:OtherIncome us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value7.5863.6533.8343.2733.9666.4135.2075.1115.2874.9977.3564.6724.5374.5054.8514.4764.6964.878125.0675.1945.3295.2795.377
Percentage of OtherIncome100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues3.57.01.61.92.12.912.32.33.04.63.02.32.32.02.62.52.83.37.04.83.33.62.93.4
Percentage of Revenues us-gaap:OperatingSegments3.67.51.61.92.13.013.12.33.14.63.02.32.42.02.72.52.93.37.04.83.43.62.93.4

us-gaap:OtherIncome us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value2.3192.4222.3962.3182.291.4410.00.00.0
Percentage of OtherIncome30.666.362.570.857.722.50.00.00.0
Percentage of Revenues1.14.61.01.31.20.70.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:AcquiredBusinesses8.18.48.38.18.07.50.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-0.0080.004-0.1140.0080.0640.0080.0180.0110.0180.0190.0190.0260.0380.0260.1090.139-0.0540.060.0190.0120.0040.0150.0050.023
Percentage of OtherIncome-0.10.1-3.00.21.60.10.30.20.30.40.30.60.80.62.23.1-1.11.20.20.20.10.30.10.4
Percentage of Revenues-0.00.0-0.00.00.00.00.00.00.00.00.00.00.00.00.10.1-0.00.00.00.00.00.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:Annuities-0.00.0-0.10.00.10.00.10.00.00.00.00.00.00.00.10.1-0.10.10.00.00.00.00.00.0

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value0.0010.0290.20.0490.020.0440.0070.0110.00.00.0160.0110.0060.0130.0820.0070.0060.0240.0330.0030.0040.0160.0150.019
Percentage of OtherIncome0.00.85.21.50.50.70.10.20.00.00.20.20.10.31.70.20.10.50.30.10.10.30.30.4
Percentage of Revenues0.00.10.10.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:DomesticLifeInsurance0.0-0.40.50.20.10.1-0.10.00.00.00.10.00.00.00.40.00.00.20.20.00.00.10.10.1

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-0.0060.0540.0070.0250.0330.0210.0480.0050.0040.030.010.0260.0210.0260.2710.010.0040.036-0.0520.005-0.0250.0860.0510.02
Percentage of OtherIncome-0.11.50.20.80.80.30.90.10.10.60.10.60.50.65.60.20.10.7-0.40.1-0.51.61.00.4
Percentage of Revenues-0.00.10.00.00.00.00.10.00.00.00.00.00.00.00.10.00.00.0-0.00.0-0.00.10.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:InternationalLifeInsurance-0.00.40.00.10.10.10.30.00.00.10.00.10.00.10.60.00.00.1-0.10.0-0.10.20.10.1

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value5.281.1441.3450.8731.5594.8995.1345.0845.2654.9487.3114.6094.4724.444.3894.324.744.758125.0475.2115.2125.2085.315
Percentage of OtherIncome69.631.335.126.739.376.498.699.599.699.099.498.798.698.690.596.5100.997.5100.099.6100.397.898.798.8
Percentage of Revenues2.42.20.60.50.82.212.12.33.04.53.02.32.32.02.42.42.83.27.04.83.43.52.83.3
Percentage of Revenues us-gaap:OperatingSegments us-gaap:AllOtherSegments37.4-129.414.116.615.442.345.748.632.952.050.150.836.338.538.548.842.149.463.254.946.651.544.551.5

None

us-gaap:PolicyholderBenefitsAndClaimsIncurredNet

us-gaap:PolicyholderBenefitsAndClaimsIncurredNet


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value333335393328205.74417211221171916171515171416191313
Percentage of PolicyholderBenefitsAndClaimsIncurredNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues15.564.115.123.117.512.948.72.510.019.65.210.39.08.89.29.69.310.59.913.410.413.07.38.2

us-gaap:PolicyholderBenefitsAndClaimsIncurredNet us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value333335393328205.74417211221171916171515171416191313
Percentage of PolicyholderBenefitsAndClaimsIncurredNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues15.564.115.123.117.512.948.72.510.019.65.210.39.08.89.29.69.310.59.913.410.413.07.38.2
Percentage of Revenues us-gaap:OperatingSegments15.768.615.323.017.413.252.22.610.219.75.310.49.38.99.39.99.510.610.013.510.713.17.58.4

us-gaap:PolicyholderBenefitsAndClaimsIncurredNet us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value1616151616100.00.00.0
Percentage of PolicyholderBenefitsAndClaimsIncurredNet49.948.344.940.650.537.90.00.00.0
Percentage of Revenues7.730.96.89.48.84.90.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:AcquiredBusinesses58.256.455.356.359.355.50.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value8.888.1897.631129.876119.292-6.7047.824103.5629.0957.7298.5538.7097.0546.2876.8125.0775.6346.6517.9481.1260.138
Percentage of PolicyholderBenefitsAndClaimsIncurredNet26.624.321.431.429.340.544.9-116.744.850.827.743.343.343.351.440.540.543.728.439.741.341.38.41.0
Percentage of Revenues4.115.63.27.25.15.221.9-3.04.510.01.44.53.93.84.73.93.84.62.85.34.35.40.60.1
Percentage of Revenues us-gaap:OperatingSegments nwli:Annuities8.753.66.715.110.310.652.2-5.28.318.52.47.66.96.58.26.96.88.25.210.17.89.51.10.1

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value4.1695.8775.0986.0993.8293.9225.9375.8395.1034.8094.7153.4835.4484.9194.2795.3384.673.6215.3653.5453.8825.1134.5883.353
Percentage of PolicyholderBenefitsAndClaimsIncurredNet12.517.514.315.311.413.928.7101.729.222.536.716.630.524.925.230.630.123.230.025.024.126.534.325.5
Percentage of Revenues1.911.22.23.52.01.814.02.62.94.41.91.72.72.22.32.92.82.43.03.32.53.52.52.1
Percentage of Revenues us-gaap:OperatingSegments nwli:DomesticLifeInsurance12.5-72.313.025.114.911.4-92.215.821.646.915.012.822.617.319.725.725.626.229.834.224.337.426.424.4

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value3.6843.3316.8695.0742.9592.1625.4616.6094.5345.7284.5828.4374.6776.2853.975.0384.5835.1687.4435.0025.5876.2057.6599.672
Percentage of PolicyholderBenefitsAndClaimsIncurredNet11.09.919.312.78.87.726.4115.126.026.835.640.126.231.823.428.929.533.141.635.334.732.257.373.5
Percentage of Revenues1.76.32.92.91.51.012.92.92.65.31.84.12.42.82.22.82.73.54.14.73.64.24.26.1
Percentage of Revenues us-gaap:OperatingSegments nwli:InternationalLifeInsurance10.823.916.615.98.95.432.014.211.919.19.318.310.612.59.311.510.913.016.816.514.715.916.425.8

None

us-gaap:InterestCreditedToPolicyholdersAccountBalances

us-gaap:InterestCreditedToPolicyholdersAccountBalances


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value61-28.02694596080-47.26112460-1.8181371078210968676249621649497359
Percentage of InterestCreditedToPolicyholdersAccountBalances100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues28.6-53.440.334.331.237.1-111.255.134.9-1.755.352.841.549.037.337.337.632.934.415.331.833.240.037.1

us-gaap:InterestCreditedToPolicyholdersAccountBalances us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value61-28.02694596080-47.26112460-1.8181371078210968676249621649497359
Percentage of InterestCreditedToPolicyholdersAccountBalances100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues28.6-53.440.334.331.237.1-111.255.134.9-1.755.352.841.549.037.337.337.632.934.415.331.833.240.037.1
Percentage of Revenues us-gaap:OperatingSegments29.0-57.240.734.231.137.9-119.255.635.5-1.756.253.442.849.537.838.438.233.434.715.432.733.441.137.6

us-gaap:InterestCreditedToPolicyholdersAccountBalances us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value334.50456333947-14.2371432.19310184597752465239441737365246
Percentage of InterestCreditedToPolicyholdersAccountBalances53.6-16.159.156.466.258.730.157.371.3-120.673.878.472.570.375.768.984.380.671.7105.274.975.470.978.5
Percentage of Revenues15.38.623.819.420.721.8-33.531.624.92.040.941.530.134.428.225.731.726.524.716.123.925.028.429.1
Percentage of Revenues us-gaap:OperatingSegments nwli:Annuities32.329.549.340.241.744.0-79.955.146.13.768.070.853.458.749.145.457.047.345.930.843.244.050.448.4

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value19-21.69324111221-20.575229.907-2.861181411167.7519.7957.2173.8437.3860.0145.464.9397.9845.803
Percentage of InterestCreditedToPolicyholdersAccountBalances31.077.425.519.021.626.543.518.016.2157.413.313.113.614.811.314.511.57.811.90.111.010.110.89.8
Percentage of Revenues8.9-41.310.36.56.79.8-48.49.95.7-2.67.46.95.77.24.25.44.32.64.10.03.53.34.33.6
Percentage of Revenues us-gaap:OperatingSegments nwli:DomesticLifeInsurance57.3267.061.546.350.562.4319.460.441.9-27.958.251.746.557.135.847.139.627.841.00.134.236.145.942.3

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value9.492-10.83714147.33711-12.456307.6-1.15179.11211168.993112.6735.68310-0.8546.9277.13136.956
Percentage of InterestCreditedToPolicyholdersAccountBalances15.438.715.424.612.214.826.424.612.563.312.98.513.814.913.116.74.311.616.4-5.314.014.518.211.7
Percentage of Revenues4.4-20.66.28.53.85.5-29.313.64.4-1.17.14.55.77.34.96.21.63.85.7-0.84.54.87.34.4
Percentage of Revenues us-gaap:OperatingSegments nwli:InternationalLifeInsurance27.7-77.835.345.822.229.9-73.165.720.0-3.835.919.825.932.721.025.76.414.323.0-2.818.218.328.818.6

None

us-gaap:OperatingExpenses us-gaap:ConsolidationItems

us-gaap:OperatingExpenses

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-09-30
Value16653197153159176201891418220618117019916014613913014889124126130
Percentage of OperatingExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues77.3102.583.788.582.681.147.384.081.175.283.589.086.089.186.780.483.787.982.184.480.485.381.7
Percentage of Revenues us-gaap:OperatingSegments78.4109.884.788.382.482.950.784.882.475.784.889.988.890.187.982.985.189.382.685.182.785.982.8

us-gaap:OperatingExpenses us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value2523232424160.00.00.0
Percentage of OperatingExpenses15.044.412.015.815.69.20.00.00.0
Percentage of Revenues11.645.610.014.012.97.50.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:AcquiredBusinesses87.583.081.684.486.684.60.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-09-30
Value80339777809117988346132133104123978991838454757881
Percentage of OperatingExpenses48.161.849.450.750.951.589.252.059.256.464.173.461.361.960.961.065.764.156.960.860.362.462.2
Percentage of Revenues37.163.441.344.942.041.842.243.748.042.453.565.352.755.252.949.155.056.346.751.348.553.250.8
Percentage of Revenues us-gaap:OperatingSegments nwli:Annuities78.4217.685.593.384.884.2100.776.289.078.889.1111.593.794.092.086.799.1100.586.998.187.893.684.5

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-09-30
Value32-8.7638242533-6.21136229.8683025242822171813188.461141513
Percentage of OperatingExpenses19.4-16.319.416.115.918.8-30.919.316.212.014.513.914.414.313.811.813.210.212.29.412.012.610.0
Percentage of Revenues15.0-16.716.314.313.115.2-14.616.213.19.112.112.412.412.712.09.511.08.910.08.09.610.78.2
Percentage of Revenues us-gaap:OperatingSegments nwli:DomesticLifeInsurance96.7107.897.6101.798.196.796.498.796.896.195.592.5102.0100.5101.883.2101.196.3100.581.793.7116.394.8

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-09-30
Value254.446342423282.27648271937173440333322273520272529
Percentage of OperatingExpenses15.38.317.715.714.916.411.325.419.524.218.39.420.220.420.923.216.221.024.222.622.319.922.7
Percentage of Revenues11.88.514.813.912.313.35.421.415.818.215.38.417.418.218.218.613.518.419.919.117.917.018.5
Percentage of Revenues us-gaap:OperatingSegments nwli:InternationalLifeInsurance74.531.984.375.571.972.113.3103.472.566.377.237.178.481.378.177.353.869.280.867.173.064.479.1

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-09-30
Value3.7770.9513.0742.384.2547.3286.1086.2227.2086.0376.3675.9276.9556.7416.9235.746.876.2699.8046.4226.86.4336.684
Percentage of OperatingExpenses2.31.81.61.62.74.130.43.35.17.43.13.34.13.44.33.94.94.86.67.25.45.15.1
Percentage of Revenues1.71.81.31.42.23.414.42.84.15.52.62.93.53.03.83.24.14.25.46.14.44.34.2
Percentage of Revenues us-gaap:OperatingSegments us-gaap:AllOtherSegments26.7-107.632.245.142.063.354.459.445.163.443.665.356.458.460.764.861.065.049.369.860.963.664.8

None

us-gaap:InterestPaidNet

us-gaap:InterestPaidNet


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value19000.019000.019000.0223000.010000.019000.010000.010000.010000.010000.010000.0
Percentage of InterestPaidNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues0.00.00.00.10.00.00.00.00.00.00.0

None

us-gaap:AllocatedShareBasedCompensationExpense

us-gaap:AllocatedShareBasedCompensationExpense


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value2400000.0-6300000.02300000.01500000.0100000.0-1500000.0-1000000.01700000.01300000.0-500000.0-600000.01300000.03600000.0800000.09000000.01700000.0-1300000.0-1500000.01700000.0-1000000.0-800000.0-800000.01900000.00
Percentage of AllocatedShareBasedCompensationExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0
Percentage of Revenues1.1-12.01.00.90.1-0.7-2.40.80.7-0.5-0.20.61.80.44.90.9-0.8-1.00.9-0.9-0.5-0.51.00.0

None

us-gaap:BenefitsLossesAndExpenses

us-gaap:BenefitsLossesAndExpenses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value15555187148150167191801347521117015918814613312612313380112116143116
Percentage of BenefitsLossesAndExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues72.0105.779.985.678.176.846.280.276.969.285.383.480.484.279.473.275.882.773.876.372.478.877.672.9

None

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value60-2.97947244250224440333633383538484025472542314143
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues28.0-5.720.114.421.923.253.819.823.130.814.716.619.615.820.626.824.217.326.223.727.621.222.427.1

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1.7290.7610.322-1.747-4.7341.0990.2351.1851.9810.041.0121.5191.6441.0610.2832.1510.1740.708-0.0480.1472.8540.2542.5721.474
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest2.9-25.50.7-7.0-11.22.21.02.64.90.12.84.54.23.00.74.40.42.7-0.10.66.70.86.23.4
Percentage of Revenues0.81.40.1-1.0-2.50.50.60.51.10.00.40.70.80.50.21.20.10.5-0.00.11.80.21.40.9
Percentage of Revenues us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

None

us-gaap:IncomeTaxExpenseBenefit

us-gaap:IncomeTaxExpenseBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value12-0.9179.6965.0038.448101.0819.0937.8776.698-3.1541213111414148.538158.90313101314
Percentage of IncomeTaxExpenseBenefit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues5.6-1.74.12.94.44.82.54.04.56.1-1.35.96.75.37.88.28.45.78.58.49.06.87.19.3

us-gaap:IncomeTaxExpenseBenefit us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value11-1.6495.1098.5379.4218.6157.3116.57111111
Percentage of IncomeTaxExpenseBenefit94.6179.8102.1101.190.694.792.898.194.083.692.4
Percentage of Revenues5.3-3.13.04.44.33.84.26.05.55.64.9
Percentage of Revenues us-gaap:OperatingSegments5.4-3.42.94.44.43.94.36.15.65.85.0

us-gaap:IncomeTaxExpenseBenefit us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value1.9181.2221.1330.9560.7470.00.00.0
Percentage of IncomeTaxExpenseBenefit15.8-133.322.611.37.20.00.00.0
Percentage of Revenues0.92.30.70.50.30.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:AcquiredBusinesses6.74.23.93.33.90.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value6.173-5.3191.3883.1554.8837.7142.4783.098-7.0073.6563.956
Percentage of IncomeTaxExpenseBenefit50.8580.027.737.347.084.831.546.3-58.227.533.2
Percentage of Revenues2.9-10.10.81.62.23.41.42.8-3.41.81.8
Percentage of Revenues us-gaap:OperatingSegments nwli:Annuities6.0-34.81.73.34.56.02.65.3-5.93.33.0

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value0.1720.188-0.1070.0890.3240.1220.1850.0981.061-0.242-0.079
Percentage of IncomeTaxExpenseBenefit1.4-20.5-2.11.13.11.32.31.58.8-1.8-0.7
Percentage of Revenues0.10.4-0.10.00.10.10.10.10.5-0.1-0.0
Percentage of Revenues us-gaap:OperatingSegments nwli:DomesticLifeInsurance0.5-2.3-0.40.30.90.30.81.03.9-1.0-0.3

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value0.9342.8041.972.0143.208-0.3222.5162.507154.9284.724
Percentage of IncomeTaxExpenseBenefit7.7-305.839.423.830.9-3.531.937.4128.537.039.6
Percentage of Revenues0.45.31.11.01.5-0.11.42.37.62.52.1
Percentage of Revenues us-gaap:OperatingSegments nwli:InternationalLifeInsurance2.720.16.26.18.0-0.76.68.433.611.29.4

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value2.292-0.5440.7252.3230.2591.1012.1320.8671.7922.792.419
Percentage of IncomeTaxExpenseBenefit18.959.314.527.52.512.127.112.914.920.920.3
Percentage of Revenues1.1-1.00.41.20.10.51.20.80.91.41.1
Percentage of Revenues us-gaap:OperatingSegments us-gaap:AllOtherSegments16.261.513.822.92.210.513.39.119.722.621.0

us-gaap:IncomeTaxExpenseBenefit us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value0.3630.160.067-0.367-0.9940.2310.050.2490.4170.0070.3550.5320.5760.3710.0990.7530.0610.248-0.0170.0510.9990.0890.9010.516
Percentage of IncomeTaxExpenseBenefit3.0-17.40.7-7.3-11.82.24.62.75.30.1-11.34.44.33.10.75.00.42.9-0.10.67.20.96.83.5
Percentage of Revenues0.20.30.0-0.2-0.50.10.10.10.20.00.10.30.30.20.10.40.00.2-0.00.00.60.10.50.3
Percentage of Revenues us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

None

us-gaap:IncomeTaxesPaidNet

us-gaap:IncomeTaxesPaidNet


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value0.0010.0012.39510240.001-0.4810.003118.283127.598475.4423150.0-10.0
Percentage of IncomeTaxesPaidNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0
Percentage of Revenues0.00.01.06.112.50.0-1.10.06.57.64.93.723.82.412.68.30.0-6.7

None

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax


None
Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-39000.05000.052000.0-86000.0553000.0127000.020000.039000.01168000.0-4000.0166000.0-86000.0-85000.0-83000.022000.0-203000.099000.098000.054000.0-53000.041000.080000.0-3000.0
Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues-0.10.00.0-0.00.30.30.00.01.1-0.00.1-0.0-0.0-0.00.0-0.10.10.10.1-0.00.00.0-0.0

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedTranslationAdjustment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value-92000.0-39000.05000.052000.0-86000.0553000.0127000.020000.039000.01168000.0-4000.0166000.0-86000.0-85000.0-83000.022000.0-202000.099000.098000.054000.0-53000.041000.080000.0
Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax0.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.099.5100.0100.0100.0100.0100.0100.0
Percentage of Revenues-0.0-0.10.00.0-0.00.30.30.00.01.1-0.00.1-0.0-0.0-0.00.0-0.10.10.10.1-0.00.00.0
Percentage of Revenues us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

None

us-gaap:OtherComprehensiveIncomeLossNetOfTax

us-gaap:OtherComprehensiveIncomeLossNetOfTax


None
Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-80.8580.131163841-2.7430.469-13.79-30.818-8.8220.4895.6713.86-35.8291.1742024-19.497-7.584-23.3829.006-5.931-8.953
Percentage of OtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues-154.10.19.520.019.2-6.50.2-7.9-28.3-3.60.22.91.7-19.40.612.516.1-10.8-7.1-15.16.1-3.2-5.6

None

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value48-2.062371933402135322639212523233326173116282128282919
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues22.4-3.916.011.517.518.451.315.818.624.716.010.712.910.512.818.615.711.617.715.318.614.415.317.814.112.5

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value45-4.8152034361933302637202121
Percentage of NetIncomeLoss94.9233.5102.0101.090.989.795.093.498.293.793.884.192.9
Percentage of Revenues21.3-9.211.817.716.846.015.017.424.215.010.010.89.7
Percentage of Revenues us-gaap:OperatingSegments21.6-9.811.717.617.149.315.217.624.315.210.111.29.9

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value3.5964.8874.4933.8312.9630.00.00.0
Percentage of NetIncomeLoss7.4-237.022.511.47.40.00.00.0
Percentage of Revenues1.79.32.62.01.40.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:AcquiredBusinesses12.517.015.613.415.40.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value22-17.9765.5811417301012-13.7187.0257.846
Percentage of NetIncomeLoss45.7871.827.943.142.386.231.846.3-62.927.633.3
Percentage of Revenues10.2-34.23.27.57.813.65.911.4-6.73.53.5
Percentage of Revenues us-gaap:OperatingSegments nwli:Annuities21.6-117.66.715.215.823.811.021.2-11.56.36.0

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value1.120.634-0.4160.4941.1270.4740.760.3962.037-0.472-0.156
Percentage of NetIncomeLoss2.3-30.7-2.11.52.81.32.31.59.3-1.9-0.7
Percentage of Revenues0.51.2-0.20.30.50.20.40.41.0-0.2-0.1
Percentage of Revenues us-gaap:OperatingSegments nwli:DomesticLifeInsurance3.3-7.8-1.71.93.31.33.23.97.5-2.0-0.5

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value8.7379.4757.8359.30711-1.5971010289.4889.37
Percentage of NetIncomeLoss18.0-459.539.227.627.8-4.532.237.5132.937.239.8
Percentage of Revenues4.018.14.54.85.1-0.76.09.214.24.84.2
Percentage of Revenues us-gaap:OperatingSegments nwli:InternationalLifeInsurance25.568.124.528.127.9-3.427.533.762.921.618.7

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value10-1.8352.8925.8794.2564.2478.7853.4793.1545.3814.798
Percentage of NetIncomeLoss21.489.014.517.410.611.927.112.914.521.120.4
Percentage of Revenues4.8-3.51.73.12.01.95.03.21.52.72.1
Percentage of Revenues us-gaap:OperatingSegments us-gaap:AllOtherSegments73.3207.654.958.036.740.654.936.634.743.641.6

us-gaap:NetIncomeLoss us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1.3660.6010.255-1.38-3.740.8680.1850.9361.5640.0330.6570.9871.0680.690.1841.3980.1130.46-0.0310.0961.8550.1651.6710.958
Percentage of NetIncomeLoss2.8-29.10.7-6.9-11.12.20.82.64.80.11.74.54.22.90.84.10.42.7-0.10.66.40.85.93.4
Percentage of Revenues0.61.10.1-0.8-1.90.40.40.40.90.00.30.50.50.30.10.80.10.3-0.00.11.20.10.90.6
Percentage of Revenues us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementClassOfStock

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value47-2.00436193239213431263821242222322516311528202727
Percentage of NetIncomeLoss97.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.2
Percentage of Revenues21.8-3.815.611.217.017.949.815.418.124.015.510.412.510.212.418.015.311.317.214.918.114.014.817.3
Percentage of Revenues us-gaap:CommonClassA0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonClassB


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1.369-0.0581.0670.5650.9531.1370.6161.0080.9180.761.120.6170.7210.6660.6680.9540.7430.4880.9050.4580.8160.6030.7950.805
Percentage of NetIncomeLoss2.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.8
Percentage of Revenues0.6-0.10.50.30.50.51.40.40.50.70.50.30.40.30.40.50.40.30.50.40.50.40.40.5
Percentage of Revenues us-gaap:CommonClassB0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value48-2.062371933402135322639212523233326173116282128
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues22.4-3.916.011.517.518.451.315.818.624.716.010.712.910.512.818.615.711.617.715.318.614.415.3
Percentage of Revenues us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

None

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:ComprehensiveIncomeNetOfTax


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value152-82.9237367282193618-3.94330223127-12.217344741128.6375.476302219
Percentage of ComprehensiveIncomeNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues70.5-158.016.121.137.537.744.816.010.7-3.612.410.915.712.2-6.619.228.227.76.98.13.520.512.012.2

None

us-gaap:Assets

us-gaap:Assets


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value12391122841255312559126121264811931120911208512126122251213812021120321189411880118011168311612115461151511462113511125910830
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Assets us-gaap:ConsolidationItems

us-gaap:CorporateNonSegment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-30
Value646567460393363342343359217217213211205199197144146150191190183207
Percentage of Assets5.24.63.73.12.92.72.93.01.81.81.71.71.71.71.71.21.21.31.71.71.61.8
Percentage of Assets5.24.63.73.12.92.72.93.01.81.81.71.71.71.71.71.21.21.31.71.71.61.8
Percentage of Assets us-gaap:CorporateNonSegment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value11744117161209212166122491230611588117321186811908120111192611816118321169711736116541153311452113541132411278111871105110657
Percentage of Assets94.895.496.396.997.197.397.197.098.298.298.398.398.398.398.398.898.898.798.698.398.398.498.698.298.4
Percentage of Assets94.895.496.396.997.197.397.197.098.298.298.398.398.398.398.398.898.898.798.698.398.398.498.698.298.4
Percentage of Assets us-gaap:OperatingSegments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Assets us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value10069729789709539400.0
Percentage of Assets8.17.97.87.77.67.40.0
Percentage of Assets8.17.97.87.77.67.40.0
Percentage of Assets us-gaap:OperatingSegments nwli:AcquiredBusinesses100.0100.0100.0100.0100.0100.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value7867791281988324846585698791892290869155926993069252929791939232919391039054899990008988893388718586
Percentage of Assets63.564.465.366.367.167.773.773.875.275.575.876.777.077.377.377.777.977.978.077.978.278.478.778.879.3
Percentage of Assets63.564.465.366.367.167.773.773.875.275.575.876.777.077.377.377.777.977.978.077.978.278.478.778.879.3
Percentage of Assets us-gaap:OperatingSegments nwli:Annuities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value14191369139913301287124312151217117311251106107110341004971961918892868831811783746705610
Percentage of Assets11.511.211.210.610.29.810.210.19.79.39.18.88.68.38.28.17.87.67.57.27.06.86.66.35.6
Percentage of Assets11.511.211.210.610.29.810.210.19.79.39.18.88.68.38.28.17.87.67.57.27.06.86.66.35.6
Percentage of Assets us-gaap:OperatingSegments nwli:DomesticLifeInsurance100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value1086110511531166117111851211122712271231123612381221123112321248125212531260126012471246125012231200
Percentage of Assets8.89.09.29.39.39.410.110.210.210.210.110.210.210.210.410.510.610.710.910.910.810.911.010.911.1
Percentage of Assets8.89.09.29.39.39.410.110.210.210.210.110.210.210.210.410.510.610.710.910.910.810.911.010.911.1
Percentage of Assets us-gaap:OperatingSegments nwli:InternationalLifeInsurance100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value363355362374372366370365381395398309307300298293289284268262264259257251260
Percentage of Assets2.92.92.93.03.02.93.13.03.23.33.32.52.62.52.52.52.52.42.32.32.32.32.32.22.4
Percentage of Assets2.92.92.93.03.02.93.13.03.23.33.32.52.62.52.52.52.52.42.32.32.32.32.32.22.4
Percentage of Assets us-gaap:OperatingSegments us-gaap:AllOtherSegments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

None

us-gaap:Liabilities

us-gaap:Liabilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value1020910253104251046710557106651003010208102381029810392103351024010283101731014510100100301000099459795
Percentage of Liabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets82.483.583.083.383.784.384.184.484.784.985.085.185.285.585.585.485.685.886.186.186.3

None

us-gaap:LiabilitiesAndStockholdersEquity

us-gaap:LiabilitiesAndStockholdersEquity


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value123911228412553125591261212648119311209112085121261222512138120211203211894118801180111683116121154611351
Percentage of LiabilitiesAndStockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

None

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value2182203021282091205519821900188318461828183218021780174917211735170016531611160015921586155615341447
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets17.616.517.016.716.315.715.915.615.315.115.014.914.814.514.514.614.414.213.913.913.813.813.713.613.4

us-gaap:StockholdersEquity us-gaap:CumulativeEffectPeriodOfAdoption, us-gaap:StatementEquityComponents

srt:CumulativeEffectPeriodOfAdoptionAdjustment, us-gaap:RetainedEarnings


None
Period End2020-03-312019-12-312019-03-312018-12-31
Value0.0-3.0320.00.0
Percentage of StockholdersEquity0.0-0.10.00.0
Percentage of Assets0.0-0.00.00.0
Percentage of Assets srt:CumulativeEffectPeriodOfAdoptionAdjustment us-gaap:RetainedEarnings0.00.00.00.0

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

nwli:AccumulatedOtherThanTemporaryImpairmentAvailableForSale


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value-0.002-0.002-0.002-0.002-0.002-0.002-0.002-0.002-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.002-0.196
Percentage of StockholdersEquity-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.00.0
Percentage of Assets-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.00.0
Percentage of Assets nwli:AccumulatedOtherThanTemporaryImpairmentAvailableForSale0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedDefinedBenefitPlansAdjustment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value-19.785-17.718-15.652-12.809-12.305-11.801-11.297-14.192-16.993-19.794-22.595-17.448-16.538-15.605-14.718-15.452-15.169-14.885-14.602-14.775-14.472-14.168-13.865-11.092-10.565-16.153
Percentage of StockholdersEquity-0.9-0.9-0.7-0.6-0.6-0.6-0.6-0.8-0.9-1.1-1.2-1.0-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.7-0.70.0
Percentage of Assets-0.2-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.2-0.2-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.10.0
Percentage of Assets us-gaap:AccumulatedDefinedBenefitPlansAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value97-8.08970675011-30.286-24.521-22.169-5.53733353427225957361232406354574691
Percentage of StockholdersEquity4.5-0.43.33.22.50.6-1.6-1.3-1.2-0.31.82.01.91.61.33.43.42.20.82.12.54.03.53.73.20.0
Percentage of Assets0.8-0.10.60.50.40.1-0.3-0.2-0.2-0.00.30.30.30.20.20.50.50.30.10.30.40.60.50.50.40.0
Percentage of Assets us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherComprehensiveIncome


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value83-20.756059434.91-37.015-34.272-34.741-20.95114202014104645240.329192750414738
Percentage of StockholdersEquity3.8-1.02.82.92.10.2-1.9-1.8-1.9-1.10.81.11.10.80.62.72.71.50.01.21.73.22.73.12.6
Percentage of Assets0.7-0.20.50.50.30.0-0.3-0.3-0.3-0.20.10.20.20.10.10.40.40.20.00.20.20.40.40.40.4
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherThanTemporaryImpairment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value-0.003-0.003-0.004-0.004-0.005-0.006-0.007-0.007-0.008-0.01-0.01-0.181-0.19-0.16-0.203-0.213-0.222-0.231-0.24-1.074-1.169-1.201-1.262-1.26-1.287-1.426
Percentage of StockholdersEquity-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.1-0.1-0.1-0.1-0.1-0.10.0
Percentage of Assets-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.00.0
Percentage of Assets us-gaap:AccumulatedOtherThanTemporaryImpairment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedTranslationAdjustment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value4.975.0625.1015.0965.0445.134.5774.454.434.3913.2232.6562.492.5762.6612.7442.7222.9242.8252.7272.6732.7262.6852.6053.2412.589
Percentage of StockholdersEquity0.20.20.20.20.20.30.20.20.20.20.20.10.10.10.20.20.20.20.20.20.20.20.20.20.20.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdditionalPaidInCapital


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value4141414141414141414141414141414141414138383838383737
Percentage of StockholdersEquity1.92.12.02.02.02.12.22.22.32.32.32.32.32.42.42.42.52.52.62.42.42.42.42.52.60.0
Percentage of Assets0.30.30.30.30.30.30.30.30.30.30.30.30.30.30.40.40.40.40.40.30.30.30.30.30.30.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value0.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0363.6363.6363.6363.6363.6363.6353.635
Percentage of StockholdersEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.20.20.20.20.20.30.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RetainedEarnings


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value20572009202619891969193618961875183918071776174017181693166916471613158715691539152214941472144413681273
Percentage of StockholdersEquity94.399.095.295.195.997.699.899.699.698.996.996.596.596.897.094.994.996.097.496.295.794.294.694.294.50.0
Percentage of Assets16.616.416.115.815.615.315.915.515.214.914.514.314.314.114.013.913.713.613.513.313.213.013.012.812.60.0
Percentage of Assets us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

None

us-gaap:EquitySecuritiesFvNi

us-gaap:EquitySecuritiesFvNi


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value17152319191917191818
Percentage of EquitySecuritiesFvNi100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.10.10.20.20.20.20.10.20.20.2

us-gaap:EquitySecuritiesFvNi nwli:PricingSource

nwli:PricedByThirdPartyVendors


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value17152319191917191818
Percentage of EquitySecuritiesFvNi100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.10.10.20.20.20.20.10.20.20.2
Percentage of Assets nwli:PricedByThirdPartyVendors0.00.00.00.00.00.00.00.00.00.0

us-gaap:EquitySecuritiesFvNi nwli:PricingSource, us-gaap:FairValueByFairValueHierarchyLevel

nwli:PricedByThirdPartyVendors, us-gaap:FairValueInputsLevel1


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value17152319191917191818
Percentage of EquitySecuritiesFvNi100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.10.10.20.20.20.20.10.20.20.2
Percentage of Assets nwli:PricedByThirdPartyVendors us-gaap:FairValueInputsLevel10.00.00.00.00.00.00.00.00.00.0

us-gaap:EquitySecuritiesFvNi us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:FairValueInputsLevel1


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value17152319191917191818
Percentage of EquitySecuritiesFvNi100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.10.10.20.20.20.20.10.20.20.2
Percentage of Assets us-gaap:FairValueInputsLevel10.00.00.00.00.00.00.00.00.00.0

us-gaap:EquitySecuritiesFvNi us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value171523191919171918
Percentage of EquitySecuritiesFvNi100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.10.10.20.20.20.20.10.20.2
Percentage of Assets us-gaap:CarryingReportedAmountFairValueDisclosure0.00.00.00.00.00.00.00.00.0

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value171523191919171918
Percentage of EquitySecuritiesFvNi100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.10.10.20.20.20.20.10.20.2
Percentage of Assets us-gaap:EstimateOfFairValueFairValueDisclosure0.00.00.00.00.00.00.00.00.0

None

us-gaap:DeferredIncomeTaxLiabilitiesNet

us-gaap:DeferredIncomeTaxLiabilitiesNet


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value55303939
Percentage of DeferredIncomeTaxLiabilitiesNet100.0100.0100.0100.0
Percentage of Assets0.40.20.30.3

None

us-gaap:StockholdersEquity

us-gaap:StockholdersEquity


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value2182203021282091205519821900188318461828183218021780174917211735170016531611160015921586155615341447
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets17.616.517.016.716.315.715.915.615.315.115.014.914.814.514.514.614.414.213.913.913.813.813.713.613.4

us-gaap:StockholdersEquity us-gaap:CumulativeEffectPeriodOfAdoption, us-gaap:StatementEquityComponents

srt:CumulativeEffectPeriodOfAdoptionAdjustment, us-gaap:RetainedEarnings


None
Period End2020-03-312019-12-312019-03-312018-12-31
Value0.0-3.0320.00.0
Percentage of StockholdersEquity0.0-0.10.00.0
Percentage of Assets0.0-0.00.00.0
Percentage of Assets srt:CumulativeEffectPeriodOfAdoptionAdjustment us-gaap:RetainedEarnings0.00.00.00.0

us-gaap:StockholdersEquity us-gaap:StatementEquityComponents

nwli:AccumulatedOtherThanTemporaryImpairmentAvailableForSale


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value-0.002-0.002-0.002-0.002-0.002-0.002-0.002-0.002-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.001-0.002-0.196
Percentage of StockholdersEquity-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.00.0
Percentage of Assets-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.00.0
Percentage of Assets nwli:AccumulatedOtherThanTemporaryImpairmentAvailableForSale0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedDefinedBenefitPlansAdjustment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value-19.785-17.718-15.652-12.809-12.305-11.801-11.297-14.192-16.993-19.794-22.595-17.448-16.538-15.605-14.718-15.452-15.169-14.885-14.602-14.775-14.472-14.168-13.865-11.092-10.565-16.153
Percentage of StockholdersEquity-0.9-0.9-0.7-0.6-0.6-0.6-0.6-0.8-0.9-1.1-1.2-1.0-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.9-0.7-0.70.0
Percentage of Assets-0.2-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.2-0.2-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.1-0.10.0
Percentage of Assets us-gaap:AccumulatedDefinedBenefitPlansAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value97-8.08970675011-30.286-24.521-22.169-5.53733353427225957361232406354574691
Percentage of StockholdersEquity4.5-0.43.33.22.50.6-1.6-1.3-1.2-0.31.82.01.91.61.33.43.42.20.82.12.54.03.53.73.20.0
Percentage of Assets0.8-0.10.60.50.40.1-0.3-0.2-0.2-0.00.30.30.30.20.20.50.50.30.10.30.40.60.50.50.40.0
Percentage of Assets us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherComprehensiveIncome


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value83-20.756059434.91-37.015-34.272-34.741-20.95114202014104645240.329192750414738
Percentage of StockholdersEquity3.8-1.02.82.92.10.2-1.9-1.8-1.9-1.10.81.11.10.80.62.72.71.50.01.21.73.22.73.12.6
Percentage of Assets0.7-0.20.50.50.30.0-0.3-0.3-0.3-0.20.10.20.20.10.10.40.40.20.00.20.20.40.40.40.4
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherThanTemporaryImpairment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value-0.003-0.003-0.004-0.004-0.005-0.006-0.007-0.007-0.008-0.01-0.01-0.181-0.19-0.16-0.203-0.213-0.222-0.231-0.24-1.074-1.169-1.201-1.262-1.26-1.287-1.426
Percentage of StockholdersEquity-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.1-0.1-0.1-0.1-0.1-0.10.0
Percentage of Assets-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.0-0.00.0
Percentage of Assets us-gaap:AccumulatedOtherThanTemporaryImpairment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedTranslationAdjustment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value4.975.0625.1015.0965.0445.134.5774.454.434.3913.2232.6562.492.5762.6612.7442.7222.9242.8252.7272.6732.7262.6852.6053.2412.589
Percentage of StockholdersEquity0.20.20.20.20.20.30.20.20.20.20.20.10.10.10.20.20.20.20.20.20.20.20.20.20.20.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AdditionalPaidInCapital


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value4141414141414141414141414141414141414138383838383737
Percentage of StockholdersEquity1.92.12.02.02.02.12.22.22.32.32.32.32.32.42.42.42.52.52.62.42.42.42.42.52.60.0
Percentage of Assets0.30.30.30.30.30.30.30.30.30.30.30.30.30.30.40.40.40.40.40.30.30.30.30.30.30.0
Percentage of Assets us-gaap:AdditionalPaidInCapital0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonStock


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value0.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0360.0363.6363.6363.6363.6363.6363.6353.635
Percentage of StockholdersEquity0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.20.20.20.20.20.30.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:CommonStock0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RetainedEarnings


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value20572009202619891969193618961875183918071776174017181693166916471613158715691539152214941472144413681273
Percentage of StockholdersEquity94.399.095.295.195.997.699.899.699.698.996.996.596.596.897.094.994.996.097.496.295.794.294.694.294.50.0
Percentage of Assets16.616.416.115.815.615.315.915.515.214.914.514.314.314.114.013.913.713.613.513.313.213.013.012.812.60.0
Percentage of Assets us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

None

us-gaap:AdditionalPaidInCapital

us-gaap:AdditionalPaidInCapital


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value414141414141414141414141414141414141413838
Percentage of AdditionalPaidInCapital100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.30.30.30.30.30.30.30.30.30.30.30.30.30.30.40.40.40.40.40.30.3

None

us-gaap:RetainedEarningsAccumulatedDeficit

us-gaap:RetainedEarningsAccumulatedDeficit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value205720092026198919691936189618751839180717761740171816931669164716131587156915391472
Percentage of RetainedEarningsAccumulatedDeficit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets16.616.416.115.815.615.315.915.515.214.914.514.314.314.114.013.913.713.613.513.313.0

None

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value83-20.756059434.91-37.015-34.272-34.741-20.95114202014104645240.3291941
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.7-0.20.50.50.30.0-0.3-0.3-0.3-0.20.10.20.20.10.10.40.40.20.00.20.4

None

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInOperatingActivities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value10210587787489104767272826238926260821039889679083
Percentage of NetCashProvidedByUsedInOperatingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues47.6201.337.045.138.741.0246.034.141.466.833.430.719.341.234.133.449.269.454.884.043.461.445.3

None

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value13613712694130267.3777259-110.978-11.252150-6.019-184.05132-130.114-27.681-75.297-79.325-98.275-271.5129
Percentage of NetCashProvidedByUsedInInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues63.0262.553.654.867.612.217.432.133.8-101.8-4.510.525.6-2.7-99.817.8-77.9-18.6-41.7-74.8-63.3-183.616.2

None

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value-140.344-144.689-131.308-142.285-155.687-156.737-135.464-120.522-87.854-98.074-24.414-22.759-67.319-50.043-4.781-9.7680.678-40.216-4.1934.83831-25.27242
Percentage of NetCashProvidedByUsedInFinancingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues-65.0-275.7-55.8-82.2-80.8-71.9-318.8-53.5-50.3-90.0-9.9-11.2-34.0-22.3-2.6-5.40.4-27.0-2.34.620.3-17.123.1

None

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect


None
Period End2020-06-302020-03-312019-06-302019-03-31
Value989848-40.04
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect100.0100.0100.0100.0
Percentage of Revenues45.6188.025.4-18.4

None

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInOperatingActivities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value10210587787489104767272826238926260821039889679083
Percentage of NetCashProvidedByUsedInOperatingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues47.6201.337.045.138.741.0246.034.141.466.833.430.719.341.234.133.449.269.454.884.043.461.445.3

None

us-gaap:NetIncomeLoss

us-gaap:NetIncomeLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value48-2.062371933402135322639212523233326173116282128282919
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues22.4-3.916.011.517.518.451.315.818.624.716.010.712.910.512.818.615.711.617.715.318.614.415.317.814.112.5

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value45-4.8152034361933302637202121
Percentage of NetIncomeLoss94.9233.5102.0101.090.989.795.093.498.293.793.884.192.9
Percentage of Revenues21.3-9.211.817.716.846.015.017.424.215.010.010.89.7
Percentage of Revenues us-gaap:OperatingSegments21.6-9.811.717.617.149.315.217.624.315.210.111.29.9

us-gaap:NetIncomeLoss us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value3.5964.8874.4933.8312.9630.00.00.0
Percentage of NetIncomeLoss7.4-237.022.511.47.40.00.00.0
Percentage of Revenues1.79.32.62.01.40.00.00.0
Percentage of Revenues us-gaap:OperatingSegments nwli:AcquiredBusinesses12.517.015.613.415.40.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value22-17.9765.5811417301012-13.7187.0257.846
Percentage of NetIncomeLoss45.7871.827.943.142.386.231.846.3-62.927.633.3
Percentage of Revenues10.2-34.23.27.57.813.65.911.4-6.73.53.5
Percentage of Revenues us-gaap:OperatingSegments nwli:Annuities21.6-117.66.715.215.823.811.021.2-11.56.36.0

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value1.120.634-0.4160.4941.1270.4740.760.3962.037-0.472-0.156
Percentage of NetIncomeLoss2.3-30.7-2.11.52.81.32.31.59.3-1.9-0.7
Percentage of Revenues0.51.2-0.20.30.50.20.40.41.0-0.2-0.1
Percentage of Revenues us-gaap:OperatingSegments nwli:DomesticLifeInsurance3.3-7.8-1.71.93.31.33.23.97.5-2.0-0.5

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value8.7379.4757.8359.30711-1.5971010289.4889.37
Percentage of NetIncomeLoss18.0-459.539.227.627.8-4.532.237.5132.937.239.8
Percentage of Revenues4.018.14.54.85.1-0.76.09.214.24.84.2
Percentage of Revenues us-gaap:OperatingSegments nwli:InternationalLifeInsurance25.568.124.528.127.9-3.427.533.762.921.618.7

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value10-1.8352.8925.8794.2564.2478.7853.4793.1545.3814.798
Percentage of NetIncomeLoss21.489.014.517.410.611.927.112.914.521.120.4
Percentage of Revenues4.8-3.51.73.12.01.95.03.21.52.72.1
Percentage of Revenues us-gaap:OperatingSegments us-gaap:AllOtherSegments73.3207.654.958.036.740.654.936.634.743.641.6

us-gaap:NetIncomeLoss us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1.3660.6010.255-1.38-3.740.8680.1850.9361.5640.0330.6570.9871.0680.690.1841.3980.1130.46-0.0310.0961.8550.1651.6710.958
Percentage of NetIncomeLoss2.8-29.10.7-6.9-11.12.20.82.64.80.11.74.54.22.90.84.10.42.7-0.10.66.40.85.93.4
Percentage of Revenues0.61.10.1-0.8-1.90.40.40.40.90.00.30.50.50.30.10.80.10.3-0.00.11.20.10.90.6
Percentage of Revenues us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementClassOfStock

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value47-2.00436193239213431263821242222322516311528202727
Percentage of NetIncomeLoss97.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.2
Percentage of Revenues21.8-3.815.611.217.017.949.815.418.124.015.510.412.510.212.418.015.311.317.214.918.114.014.817.3
Percentage of Revenues us-gaap:CommonClassA0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonClassB


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1.369-0.0581.0670.5650.9531.1370.6161.0080.9180.761.120.6170.7210.6660.6680.9540.7430.4880.9050.4580.8160.6030.7950.805
Percentage of NetIncomeLoss2.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.8
Percentage of Revenues0.6-0.10.50.30.50.51.40.40.50.70.50.30.40.30.40.50.40.30.50.40.50.40.40.5
Percentage of Revenues us-gaap:CommonClassB0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NetIncomeLoss us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value48-2.062371933402135322639212523233326173116282128
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues22.4-3.916.011.517.518.451.315.818.624.716.010.712.910.512.818.615.711.617.715.318.614.415.3
Percentage of Revenues us-gaap:RetainedEarnings0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

None

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value13613712694130267.3777259-110.978-11.252150-6.019-184.05132-130.114-27.681-75.297-79.325-98.275-271.5129
Percentage of NetCashProvidedByUsedInInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues63.0262.553.654.867.612.217.432.133.8-101.8-4.510.525.6-2.7-99.817.8-77.9-18.6-41.7-74.8-63.3-183.616.2

None

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment

us-gaap:PaymentsToAcquirePropertyPlantAndEquipment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value0.2170.0580.3471.4950.9250.0770.0680.0820.4352.5537.4191.4640.1890.044500.00.00.0
Percentage of PaymentsToAcquirePropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.00.0

None

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value-140.344-144.689-131.308-142.285-155.687-156.737-135.464-120.522-87.854-98.074-24.414-22.759-67.319-50.043-4.781-9.7680.678-40.216-4.1934.83831-25.27242
Percentage of NetCashProvidedByUsedInFinancingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Revenues-65.0-275.7-55.8-82.2-80.8-71.9-318.8-53.5-50.3-90.0-9.9-11.2-34.0-22.3-2.6-5.40.4-27.0-2.34.620.3-17.123.1

None

us-gaap:Dividends

us-gaap:Dividends


None
Period End2020-06-302020-03-312019-06-302019-03-312018-06-302018-03-312017-09-302017-06-30
Value0.00.00.00.0-3.03.04.04.0
Percentage of Dividends0.00.00.00.0100.0100.0100.0100.0

us-gaap:Dividends dei:LegalEntity

nwli:NISFinancialServicesInc


None
Period End2020-03-31
Value0.9
Percentage of Dividends0.0

us-gaap:Dividends us-gaap:StatementClassOfStock

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value0.00.01.2370.00.00.01.2370.00.00.01.2370.00.00.01.2370.00.00.01.2370.00.00.00.0011.236
Percentage of Dividends0.00.00.00.00.00.00.00.0-0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:CommonClassB


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value0.00.00.0360.00.00.00.0360.00.00.00.0360.00.00.00.0360.00.00.00.0360.00.00.00.00.036
Percentage of Dividends0.00.00.00.00.00.00.00.0-0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

None

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value0000000003000.018018.019018.019018.019168.019268.027268.027768.027768.027768.028768.029768.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber0.00.00.00.00.00.00.00.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

None

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value000000000208.05242.07240.28240.28240.39240.47243.04243.26243.26243.26242.04242.48
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice0.00.00.00.00.00.00.00.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

None

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents


None
Period End2020-06-302020-03-312019-12-312019-06-302019-03-312018-12-312017-12-312016-12-31
Value4503522531409113121751
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents100.0100.0100.0100.0100.0100.0100.0100.0

nwli:AmortizationOfUnrealizedGainLossOfAvailableForSaleSecuritiesTransferredToHoldToMaturitySecurities us-gaap:StatementEquityComponents

nwli:AmortizationOfUnrealizedGainLossOfAvailableForSaleSecuritiesTransferredToHoldToMaturitySecurities

us-gaap:AccumulatedOtherThanTemporaryImpairment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1000.02000.01000.02000.02000.02000.02000.02000.03000.02000.0-287000.017000.0-57000.085000.020000.018000.017000.017000.0-386000.0185000.068000.0104000.04000.0
Percentage of AmortizationOfUnrealizedGainLossOfAvailableForSaleSecuritiesTransferredToHoldToMaturitySecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:ChangeInNetUnrealizedGainLossOnInvestmentSecuritiesHavingCreditLossesRecognizedInConsolidatedStatementOfIncomeNetofTax

nwli:ChangeInNetUnrealizedGainLossOnInvestmentSecuritiesHavingCreditLossesRecognizedInConsolidatedStatementOfIncomeNetofTax


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value0-1000.00-1000.0-1000.0-1000.000-2000.00-173000.0-9000.030000.0-43000.0-10000.0-9000.0-9000.0-9000.0-834000.0-95000.0-32000.0-61000.02000.023000.0
Percentage of ChangeInNetUnrealizedGainLossOnInvestmentSecuritiesHavingCreditLossesRecognizedInConsolidatedStatementOfIncomeNetofTax0.0100.00.0100.0100.0100.00.00.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:ChangeInShadowDeferredPolicy us-gaap:StatementEquityComponents

nwli:ChangeInShadowDeferredPolicy

nwli:AccumulatedOtherThanTemporaryImpairmentAvailableForSale


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value00000001000.0000000000000000
Percentage of ChangeInShadowDeferredPolicy0.00.00.00.00.00.00.0100.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherThanTemporaryImpairment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1000.01000.01000.01000.01000.01000.02000.01000.01000.02000.0171000.08000.0-27000.042000.010000.09000.08000.08000.0793000.090000.036000.043000.06000.0
Percentage of ChangeInShadowDeferredPolicy0.00.00.00.00.00.00.0100.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwli:DeferralAndAmortizationOfSalesInducementsNoncashOperatingActivity

nwli:DeferralAndAmortizationOfSalesInducementsNoncashOperatingActivity


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value3.2913.363.6944.6794.7174.1054.601
Percentage of DeferralAndAmortizationOfSalesInducementsNoncashOperatingActivity100.0100.0100.0100.0100.0100.0100.0

nwli:DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense

nwli:DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value313030223132242631
Percentage of DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value313030223132242631
Percentage of DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-30
Value1.7032.3912.0182.1762.4061.7480.00.0
Percentage of DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense5.58.06.79.57.75.40.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value191918211819181721
Percentage of DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense62.263.362.694.359.761.373.665.367.7

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value3.2092.5732.8992.1813.3073.413.1772.9782.709
Percentage of DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense10.38.69.69.510.510.612.911.18.7

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value6.8446.0526.398-3.0476.9487.2943.3356.3077.336
Percentage of DeferredPolicyAcquisitionCostsAndValueOfBusinessAcquiredAmortizationExpense22.020.121.2-13.222.122.713.523.623.6

nwli:HeldToMaturitySecuritiesRealizedGainsOnDisposal

nwli:HeldToMaturitySecuritiesRealizedGainsOnDisposal


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value1395000.02724000.01246000.0924000.027000.01090000.0734000.0571000.0555000.01982000.01557000.0
Percentage of HeldToMaturitySecuritiesRealizedGainsOnDisposal100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:HeldToMaturitySecuritiesRealizedLossesOnDisposal

nwli:HeldToMaturitySecuritiesRealizedLossesOnDisposal


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-31
Value00000019000.00035000.034000.0
Percentage of HeldToMaturitySecuritiesRealizedLossesOnDisposal0.00.00.00.00.00.0100.00.00.0100.0100.0

nwli:IncreaseDecreaseInDebtSecuritiesAvailableForSaleAndHeldtomaturityAllowanceforCreditLoss

nwli:IncreaseDecreaseInDebtSecuritiesAvailableForSaleAndHeldtomaturityAllowanceforCreditLoss


None
Period End2020-06-302020-03-312019-06-302019-03-31
Value-757000.03411000.000
Percentage of IncreaseDecreaseInDebtSecuritiesAvailableForSaleAndHeldtomaturityAllowanceforCreditLoss100.0100.00.00.0

nwli:IncreaseDecreaseInDeferredPolicyAcquisitionCostsSalesInducementCostsAndValueOfBusinessAcquired

nwli:IncreaseDecreaseInDeferredPolicyAcquisitionCostsSalesInducementCostsAndValueOfBusinessAcquired


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
Value-19463000.0-16681000.0-15339000.0-11185000.0-22310000.0-20342000.0-11834000.0-10341000.0
Percentage of IncreaseDecreaseInDeferredPolicyAcquisitionCostsSalesInducementCostsAndValueOfBusinessAcquired100.0100.0100.0100.0100.0100.0100.0100.0

nwli:InvestmentsPercentageOfGainsOnBondsDueToCallsOfSecurities

nwli:InvestmentsPercentageOfGainsOnBondsDueToCallsOfSecurities


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-31
Value0.9990.9960.9960.8940.4140.9730.9990.991.00.990.630.950.9950.360.84-0.0790.75
Percentage of InvestmentsPercentageOfGainsOnBondsDueToCallsOfSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:NoncashorPartNoncashAcquisitionContingentConsiderationLiability

nwli:NoncashorPartNoncashAcquisitionContingentConsiderationLiability


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value00111000.094000.0171000.03700000.00000
Percentage of NoncashorPartNoncashAcquisitionContingentConsiderationLiability0.00.0100.0100.0100.0100.00.00.00.00.0

nwli:OtherComprehensiveIncomeLossSecuritiesAdjustmentsAndOtherThanTemporaryImpairmentLossesPortionAttributableToParent

nwli:OtherComprehensiveIncomeLossSecuritiesAdjustmentsAndOtherThanTemporaryImpairmentLossesPortionAttributableToParent


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value105-78.753163941-2.352-16.63-34.7871.2336.69
Percentage of OtherComprehensiveIncomeLossSecuritiesAdjustmentsAndOtherThanTemporaryImpairmentLossesPortionAttributableToParent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:PaymentstoAcquireEquitySecuritiesFVNI

nwli:PaymentstoAcquireEquitySecuritiesFVNI


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value135000.0488000.0365000.0682000.033000.0262000.0764000.01272000.030000.0376000.0
Percentage of PaymentstoAcquireEquitySecuritiesFVNI100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:PremiumsEarnedAndPolicyCharges

nwli:PremiumsEarnedAndPolicyCharges


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value595861616055434244424245444545444646464443414341
Percentage of PremiumsEarnedAndPolicyCharges100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:PremiumsEarnedAndPolicyCharges us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value595861616055434244424245444545444646464443414341
Percentage of PremiumsEarnedAndPolicyCharges100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:PremiumsEarnedAndPolicyCharges us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value1920202020130.00.00.0
Percentage of PremiumsEarnedAndPolicyCharges33.334.132.732.533.624.90.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value4.6994.654.2565.3365.8574.8685.6525.5977.2985.1474.1085.2936.0545.2364.8135.3916.285.7365.1425.9836.2064.845.6895.126
Percentage of PremiumsEarnedAndPolicyCharges7.97.96.98.69.68.813.013.216.312.19.611.613.511.510.612.013.512.411.113.614.311.613.112.5

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1211121110101110109.6019.5659.9079.0668.8499.9148.5078.6487.6598.068.2597.9376.4876.7246.847
Percentage of PremiumsEarnedAndPolicyCharges20.119.120.718.417.619.525.523.722.522.522.321.720.219.421.918.918.716.617.518.818.215.615.516.7

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value232224252326262627272930293130313132322929303029
Percentage of PremiumsEarnedAndPolicyCharges38.738.939.740.539.246.961.463.261.265.468.266.666.369.167.469.167.871.071.467.667.572.871.470.9

nwli:RealizedInvestmentGainsLossesNetOfTax us-gaap:ConsolidationItems

nwli:RealizedInvestmentGainsLossesNetOfTax

us-gaap:MaterialReconcilingItems


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value2469000.02753000.02005000.0-396000.0-336000.03657000.02244000.01797000.02130000.0483000.02507000.01348000.04061000.01680000.0
Percentage of RealizedInvestmentGainsLossesNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:RealizedInvestmentGainsLossesTax us-gaap:ConsolidationItems

nwli:RealizedInvestmentGainsLossesTax

us-gaap:MaterialReconcilingItems


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value656000.0732000.0534000.0-106000.0-89000.0972000.0597000.0478000.0566000.0128000.01350000.0726000.02186000.0905000.0
Percentage of RealizedInvestmentGainsLossesTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:SharebasedCompensationArrangementbySharebasedPaymentAwardPerformanceFactorPercentageOfPredefinedMetricTarget us-gaap:AwardType

nwli:SharebasedCompensationArrangementbySharebasedPaymentAwardPerformanceFactorPercentageOfPredefinedMetricTarget

us-gaap:PerformanceShares


None
Period End2020-03-312019-03-31
Value1.01190.9386
Percentage of SharebasedCompensationArrangementbySharebasedPaymentAwardPerformanceFactorPercentageOfPredefinedMetricTarget100.0100.0

nwli:SharebasedPaymentArrangementOptionExercisePriceRange us-gaap:AwardType, us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

nwli:SharebasedPaymentArrangementOptionExercisePriceRange

us-gaap:StockAppreciationRightsSARS, nwli:ExercisePriceRange10


None
Period End2020-06-302020-03-31
Value0252.91
Percentage of SharebasedPaymentArrangementOptionExercisePriceRange0.0100.0

us-gaap:StockAppreciationRightsSARS, nwli:ExercisePriceRange3


None
Period End2020-06-302020-03-31
Value0132.56
Percentage of SharebasedPaymentArrangementOptionExercisePriceRange0.052.4

us-gaap:StockAppreciationRightsSARS, nwli:ExercisePriceRange4


None
Period End2020-06-302020-03-31
Value0210.22
Percentage of SharebasedPaymentArrangementOptionExercisePriceRange0.083.1

us-gaap:StockAppreciationRightsSARS, nwli:ExercisePriceRange5


None
Period End2020-06-302020-03-31
Value0216.48
Percentage of SharebasedPaymentArrangementOptionExercisePriceRange0.085.6

us-gaap:StockAppreciationRightsSARS, nwli:ExercisePriceRange6


None
Period End2020-06-302020-03-31
Value0311.16
Percentage of SharebasedPaymentArrangementOptionExercisePriceRange0.0123.0

us-gaap:StockAppreciationRightsSARS, nwli:ExercisePriceRange7


None
Period End2020-06-302020-03-31
Value0310.55
Percentage of SharebasedPaymentArrangementOptionExercisePriceRange0.0122.8

us-gaap:StockAppreciationRightsSARS, nwli:ExercisePriceRange8


None
Period End2020-06-302020-03-31
Value0334.34
Percentage of SharebasedPaymentArrangementOptionExercisePriceRange0.0132.2

us-gaap:StockAppreciationRightsSARS, nwli:ExercisePriceRange9


None
Period End2020-06-302020-03-31
Value0303.77
Percentage of SharebasedPaymentArrangementOptionExercisePriceRange0.0120.1

nwli:TraditionalLifePremium

nwli:TraditionalLifePremium


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value2223242423175.0094.2094.9284.1455.3235.285
Percentage of TraditionalLifePremium100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccretionAmortizationOfDiscountsAndPremiumsInvestments

us-gaap:AccretionAmortizationOfDiscountsAndPremiumsInvestments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value-387000.0-850000.0-466000.0-436000.0-872000.0-490000.0338000.0-64000.0273000.0-123000.0589000.0-87000.0-105000.0-116000.0227000.0-47000.0-27000.023000.0-516000.093000.0-106000.04000.0-178000.0
Percentage of AccretionAmortizationOfDiscountsAndPremiumsInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisitionsProFormaNetIncomeLoss us-gaap:BusinessAcquisition

us-gaap:BusinessAcquisitionsProFormaNetIncomeLoss

nwli:OzarkNationalLifeInsuranceCompany


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value48-2.062193341393631
Percentage of BusinessAcquisitionsProFormaNetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisitionsProFormaRevenue us-gaap:BusinessAcquisition

us-gaap:BusinessAcquisitionsProFormaRevenue

nwli:OzarkNationalLifeInsuranceCompany


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value21652173192227254203138
Percentage of BusinessAcquisitionsProFormaRevenue100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleRealizedGain

us-gaap:DebtSecuritiesAvailableForSaleRealizedGain


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1730000.0761000.01250000.0197000.01168000.01183000.0235000.01191000.01981000.040000.01071000.01529000.01635000.0
Percentage of DebtSecuritiesAvailableForSaleRealizedGain100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleRealizedLoss

us-gaap:DebtSecuritiesAvailableForSaleRealizedLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value00927000.00084000.006000.0007000.000
Percentage of DebtSecuritiesAvailableForSaleRealizedLoss0.00.0100.00.00.0100.00.0100.00.00.0100.00.00.0

us-gaap:DebtSecuritiesHeldToMaturityCreditLossExpenseReversal

us-gaap:DebtSecuritiesHeldToMaturityCreditLossExpenseReversal


None
Period End2020-06-30
Value1099000.0
Percentage of DebtSecuritiesHeldToMaturityCreditLossExpenseReversal100.0

us-gaap:DebtSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairment

us-gaap:DebtSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairment


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value3.1253.485-0.502-0.4254.6292.2752.6960.6112.0746.247
Percentage of DebtSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanAmortizationOfGainsLosses us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAmortizationOfGainsLosses

us-gaap:OtherPensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value-1445000.0-1445000.0-347000.0-348000.0-348000.0-348000.0-176000.0-176000.0-176000.0-176000.0-819000.0-818000.0-819000.0-818000.0-500000.0-501000.0
Percentage of DefinedBenefitPlanAmortizationOfGainsLosses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value-39000.0-40000.0-61000.0-61000.0-61000.0-61000.0-38000.0-38000.0-38000.0-37000.0-10000.0-10000.0-21000.0000
Percentage of DefinedBenefitPlanAmortizationOfGainsLosses2.72.817.617.517.517.521.621.621.621.01.21.22.6-0.0-0.0-0.0

us-gaap:PensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value-145000.0-145000.0-165000.0-165000.0-165000.0-165000.0-131000.0-131000.0-131000.0-131000.0-161000.0-159000.0-159000.0-159000.0-193000.0-193000.0
Percentage of DefinedBenefitPlanAmortizationOfGainsLosses10.010.047.647.447.447.474.474.474.474.419.719.419.419.438.638.5

us-gaap:DefinedBenefitPlanAmortizationOfPriorServiceCostCredit us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanAmortizationOfPriorServiceCostCredit

us-gaap:OtherPensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value15000.015000.015000.014000.015000.015000.014000.015000.015000.015000.014000.015000.015000.015000.014000.015000.0
Percentage of DefinedBenefitPlanAmortizationOfPriorServiceCostCredit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value0013000.013000.013000.013000.025000.026000.026000.026000.026000.025000.026000.026000.025000.026000.0
Percentage of DefinedBenefitPlanAmortizationOfPriorServiceCostCredit0.00.086.792.986.786.7178.6173.3173.3173.3185.7166.7173.3173.3178.6173.3

us-gaap:DefinedBenefitPlanContributionsByEmployer us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanContributionsByEmployer

us-gaap:OtherPensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value500000.0400000.0382000.0700000.0500000.0400000.0382000.0700000.0500000.0400000.0382000.0
Percentage of DefinedBenefitPlanContributionsByEmployer100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value100000.0100000.0569000.00000100000.000106000.0
Percentage of DefinedBenefitPlanContributionsByEmployer20.025.0149.00.00.00.00.014.30.00.027.7

us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets

us-gaap:PensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value316000.0315000.0271000.0271000.0272000.0272000.0325000.0325000.0325000.0325000.0307000.0306000.0307000.0307000.0303000.0304000.0
Percentage of DefinedBenefitPlanExpectedReturnOnPlanAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DefinedBenefitPlanInterestCost us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanInterestCost

us-gaap:OtherPensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value337000.0338000.0257000.0256000.0256000.0256000.0213000.0213000.0213000.0213000.0346000.0347000.0347000.0347000.0264000.0265000.0
Percentage of DefinedBenefitPlanInterestCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value42000.041000.050000.049000.050000.049000.038000.040000.040000.040000.035000.035000.039000.030000.031000.030000.0
Percentage of DefinedBenefitPlanInterestCost12.512.119.519.119.519.117.818.818.818.810.110.111.28.611.711.3

us-gaap:PensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value169000.0168000.0209000.0210000.0210000.0210000.0224000.0225000.0225000.0225000.0239000.0240000.0239000.0239000.0250000.0250000.0
Percentage of DefinedBenefitPlanInterestCost50.149.781.382.082.082.0105.2105.6105.6105.669.169.268.968.994.794.3

us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost

us-gaap:OtherPensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value2100000.02100000.0744000.0744000.0745000.0744000.0494000.0494000.0494000.0494000.01385000.01384000.01385000.01384000.0889000.0890000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherPostretirementBenefitPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value81000.081000.0124000.0123000.0124000.0123000.0101000.0104000.0104000.0103000.071000.070000.086000.056000.056000.056000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost3.93.916.716.516.616.520.421.121.120.95.15.16.24.06.36.3

us-gaap:PensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value25000.025000.0127000.0128000.0127000.0127000.057000.059000.059000.059000.0118000.0120000.0118000.0118000.0166000.0165000.0
Percentage of DefinedBenefitPlanNetPeriodicBenefitCost1.21.217.117.217.017.111.511.911.911.98.58.78.58.518.718.5

us-gaap:DefinedBenefitPlanServiceCost us-gaap:RetirementPlanType

us-gaap:DefinedBenefitPlanServiceCost

us-gaap:OtherPensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value303000.0302000.0125000.0126000.0126000.0125000.091000.090000.090000.090000.0206000.0204000.0204000.0204000.0111000.0109000.0
Percentage of DefinedBenefitPlanServiceCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PensionPlansDefinedBenefit


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value27000.027000.024000.024000.024000.024000.027000.028000.028000.028000.025000.027000.027000.027000.026000.026000.0
Percentage of DefinedBenefitPlanServiceCost8.98.919.219.019.019.229.731.131.131.112.113.213.213.223.423.9

us-gaap:DepreciationAmortizationAndAccretionNet

us-gaap:DepreciationAmortizationAndAccretionNet


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value2.8912.8853.0852.7211.0094.4553.0562.8372.9113.0212.6262.4172.4882.4742.2341.8112.0271.9850.670.6460.830.8410.899
Percentage of DepreciationAmortizationAndAccretionNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeGainLossOnDerivativeNet us-gaap:DerivativeInstrumentRisk, us-gaap:HedgingDesignation, us-gaap:IncomeStatementLocation

us-gaap:DerivativeGainLossOnDerivativeNet

nwli:EquityIndexOptions, us-gaap:Nondesignated, us-gaap:InvestmentIncome


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value40-106.629603.2961742-115.5856910-44.3948445326120192.094-12.9018.134-52.816-8.782-8.287193.479
Percentage of DerivativeGainLossOnDerivativeNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:FixedIndexProducts, us-gaap:Nondesignated, nwli:UniversalLifeAndAnnuityContractInterest


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-23.7967-54.4873.533-13.439-27.03296-63.602-9.35742-89.067-48.168-36.422-63.624-16.081-12.1946.11711-1.526418.8411-20.477-4.033
Percentage of DerivativeGainLossOnDerivativeNet-59.1-63.4-90.7107.2-75.4-64.4-83.4-91.3-90.9-96.6-105.6-106.7-113.1-104.0-80.2-63.8292.1-90.9-18.8-79.2-100.7-139.9-105.9-115.9

us-gaap:DerivativeGainLossOnDerivativeNet us-gaap:HedgingDesignation

us-gaap:Nondesignated


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value16-38.9765.5936.8294.38914-19.1766.0810.935-1.509-4.744-3.037-4.207-2.4183.9766.928.211-1.1796.608-10.9770.0583.309-1.139-0.554
Percentage of DerivativeGainLossOnDerivativeNet40.936.69.3207.224.635.616.68.79.13.4-5.6-6.7-13.1-4.019.836.2392.19.181.220.8-0.7-39.9-5.9-15.9

us-gaap:EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents


None
Period End2020-06-302020-03-312019-06-302019-03-31
Value-116000.0-50000.0-109000.0700000.0
Percentage of EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents100.0100.0100.0100.0

us-gaap:EmbeddedDerivativeGainLossOnEmbeddedDerivativeNet

us-gaap:EmbeddedDerivativeGainLossOnEmbeddedDerivativeNet


None
Period End2020-06-302020-03-312019-06-302019-03-31
Value-3.729-4.7-15.7
Percentage of EmbeddedDerivativeGainLossOnEmbeddedDerivativeNet100.0100.0100.0100.0

us-gaap:EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense

us-gaap:EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value500000.0-1300000.0500000.0300000.00-300000.0-200000.0400000.0300000.0-100000.0-200000.0-500000.0-1200000.0-300000.02400000.0-600000.0500000.0500000.0-1200000.0400000.0300000.0300000.0700000.00
Percentage of EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0

us-gaap:EquitySecuritiesFvNiGainLoss

us-gaap:EquitySecuritiesFvNiGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1826000.0-5816000.01412000.0301000.0387000.01951000.0-1789000.000-541000.0-87000.0-10000.08000.0
Percentage of EquitySecuritiesFvNiGainLoss100.0100.0100.0100.0100.0100.0100.00.00.0100.0100.0100.0100.0

us-gaap:FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss

us-gaap:FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value62-105.99737-2.024.3540-114.4696520-44.3373516125429232.1-11.36219-51.707-11.922-6.843100.747
Percentage of FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss us-gaap:FairValueByAssetClass

nwli:DerivativesIndexOptions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value62-105.99737-2.024.3540-114.4696520-44.3373516125429232.1-11.36219-51.707-11.922-6.843100.747
Percentage of FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss us-gaap:FairValueByAssetClass, us-gaap:IncomeStatementLocation

nwli:DerivativesIndexOptions, nwli:NetInvestmentIncome


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value62-105.99737-2.024.3540-114.4696520-44.3373516125429232.1-11.36219-51.707-11.922-6.843100.747
Percentage of FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss us-gaap:IncomeStatementLocation

nwli:NetInvestmentIncome


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value62-105.99737-2.024.3540-114.4696520-44.3373516125429232.1-11.36219-51.707-11.922-6.843100.747
Percentage of FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss

us-gaap:FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value60-112.19240-0.4644.61438-115.6016721-44.883417155537250.458-13.064-46.059-1.048-0.813-0.787410.175
Percentage of FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss us-gaap:FairValueByLiabilityClass

nwli:ContingentConsideration


None
Period End2020-06-302019-06-30
Value-4.1740.171
Percentage of FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss-6.93.7

nwli:PolicyholderAccountBalances


None
Period End2020-06-302019-06-30
Value624.35
Percentage of FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss102.994.3

us-gaap:EmployeeStock


None
Period End2020-06-302019-06-30
Value2.4440.093
Percentage of FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss4.02.0

us-gaap:FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss us-gaap:FairValueByLiabilityClass, us-gaap:IncomeStatementLocation

nwli:ContingentConsideration, us-gaap:OtherOperatingIncomeExpense


None
Period End2020-06-302019-06-30
Value-4.1740.171
Percentage of FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss-6.93.7

nwli:PolicyholderAccountBalances, us-gaap:OtherOperatingIncomeExpense


None
Period End2020-06-302019-06-30
Value624.35
Percentage of FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss102.994.3

us-gaap:EmployeeStock, us-gaap:OtherOperatingIncomeExpense


None
Period End2020-06-302019-06-30
Value2.4440.093
Percentage of FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss4.02.0

us-gaap:FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss us-gaap:IncomeStatementLocation

us-gaap:OtherOperatingIncomeExpense


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value60-112.19240-0.4644.61438-115.6016721-44.883417155537250.458-13.064-46.059-1.048-0.813-0.787410.175
Percentage of FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value40-106.629603.2961742-115.5856910-44.3948445326120192.094-12.9018.134-52.816-8.782-8.287193.479
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 us-gaap:FairValueByAssetClass

nwli:DerivativesIndexOptions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value40-106.629603.2961742-115.5856910-44.3948445326120192.094-12.9018.134-52.816-8.782-8.287193.479
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value162220191917231921222019181619181918212421182019
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases us-gaap:FairValueByAssetClass

nwli:DerivativesIndexOptions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value162220191917231921222019181619181918212421182019
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1449296.704173.27829544656735051488.988110.01.822161936283559
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements us-gaap:FairValueByAssetClass

nwli:DerivativesIndexOptions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1449296.704173.27829544656735051488.988110.01.822161936283559
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-22.06-73.84856-1.9781325-97.5426510-43.428884839642313-7.76-13.4233.247-42.887-9.653-12.383224.099
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings us-gaap:FairValueByLiabilityClass

nwli:ContingentConsideration


None
Period End2020-06-302019-06-30
Value4.174-0.171
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings-18.9-1.2

nwli:PolicyholderAccountBalances


None
Period End2020-06-302019-06-30
Value-23.79-13.44
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings107.8-98.1

us-gaap:EmployeeStock


None
Period End2020-06-302019-06-30
Value-2.444-0.093
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings11.1-0.7

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value00115000.0003700000.074000.0000413000.0531000.0515000.0230000.01167000.0388000.0309000.00000000
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues0.00.0100.00.00.0100.0100.00.00.00.0100.0100.0100.0100.0100.0100.0100.00.00.00.00.00.00.00.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value162220191917231921222019181619181918212421182019
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases us-gaap:FairValueByLiabilityClass

nwli:PolicyholderAccountBalances


None
Period End2020-06-302019-06-30
Value1619
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1450296.704175.8325446577450524812110.0091.628161936283560
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements us-gaap:FairValueByLiabilityClass

nwli:PolicyholderAccountBalances


None
Period End2020-06-302019-06-30
Value1417
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements99.8100.0

us-gaap:EmployeeStock


None
Period End2020-06-302019-06-30
Value0.0280.0
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements0.20.0

us-gaap:GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments

us-gaap:GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value3.1253.4852.5391.4435.4774.6292.8412.2752.6960.6113.9692.0746.2472.5852.4815.4262.7822.3811.3050.8134.3650.9784.9732.169
Percentage of GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1.7290.7610.3220.1981.1681.0990.2351.1851.9810.041.1241.5191.6441.0610.2832.1510.1740.7080.0970.1472.9610.2542.6871.474
Percentage of GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments55.321.812.713.721.323.78.352.173.56.528.373.226.341.011.439.66.329.77.418.167.826.054.068.0

us-gaap:GainsLossesOnSalesOfInvestmentRealEstate

us-gaap:GainsLossesOnSalesOfInvestmentRealEstate


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value0023000.003385000.03503000.01799000.0000002657000.0049000.001611000.01290000.000001000.0820000.0
Percentage of GainsLossesOnSalesOfInvestmentRealEstate0.00.0100.00.0100.0100.0100.00.00.00.00.00.0100.00.0100.00.0100.0100.00.00.00.00.0100.0100.0

us-gaap:ImpairmentOfInvestments

us-gaap:ImpairmentOfInvestments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-2000.0-2000.07000.01943000.05900000.0-3000.09000.0-3000.0-3000.0-3000.0-418000.0-26000.0-23000.0-20000.0-30000.0-27000.0-27000.0-26000.0-2359000.0-284000.02000.0-160000.0-14000.00
Percentage of ImpairmentOfInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0

us-gaap:IncreaseDecreaseInAccruedIncomeTaxesPayable

us-gaap:IncreaseDecreaseInAccruedIncomeTaxesPayable


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value14-17.0315-1.409-11.21919-19.93915-3.021-13.451106.535-32.68617-8.36-0.78912106.855-11.821-7.588-3.294
Percentage of IncreaseDecreaseInAccruedIncomeTaxesPayable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInAccruedInvestmentIncomeReceivable

us-gaap:IncreaseDecreaseInAccruedInvestmentIncomeReceivable


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value-4712000.02482000.0-5320000.062000.0-7094000.03195000.0-4725000.02384000.0-1105000.02966000.0-6220000.05004000.0-3948000.02737000.0-1992000.02274000.0-3077000.02421000.0-1100000.01281000.0-2107000.05418000.0-4129000.0
Percentage of IncreaseDecreaseInAccruedInvestmentIncomeReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInDeferredIncomeTaxes

us-gaap:IncreaseDecreaseInDeferredIncomeTaxes


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value2.614-15.9717.7924.1964.4838.823-21.7586.6870.497-11.864252.0891.262110.435-0.673-1.378-8.536-8.97-15.312-7.408-8.3270.87
Percentage of IncreaseDecreaseInDeferredIncomeTaxes100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInFuturePolicyBenefitReserves

us-gaap:IncreaseDecreaseInFuturePolicyBenefitReserves


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value4.1066.3576.7986.1911.545-0.776-0.908-12.955-1.2052.5941.078-0.1322.5774.1715.583.941-1.1620.6295.3694.2992.717-0.1293.742
Percentage of IncreaseDecreaseInFuturePolicyBenefitReserves100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOtherOperatingAssets

us-gaap:IncreaseDecreaseInOtherOperatingAssets


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1.28-9.39912-3.0370.9671.79-6.4214.4180.4367.635-0.9934.4550.9172.39-3.850.313.561-0.1886.351-0.36-0.2897.2270.895
Percentage of IncreaseDecreaseInOtherOperatingAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOtherOperatingLiabilities

us-gaap:IncreaseDecreaseInOtherOperatingLiabilities


None
Period End2020-06-302020-03-312019-06-302019-03-31
Value2.566-8.775-1.72-4.142
Percentage of IncreaseDecreaseInOtherOperatingLiabilities100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOtherPolicyholderFunds

us-gaap:IncreaseDecreaseInOtherPolicyholderFunds


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1.2916.972-2.108-12.016-7.078-0.7536.165-3.815-3.7669.101-9.063-9.181-6.4229.284-6.6960.785-4.897-1.0638.6592.824-9.6114-2.953
Percentage of IncreaseDecreaseInOtherPolicyholderFunds100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent


None
Period End2020-06-302019-06-30
Value-92000.0-86000.0
Percentage of OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent100.0100.0

us-gaap:OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax

us-gaap:OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-2.067-2.066-2.843-0.504-0.504-0.5042.8952.8012.8012.801-1.143-0.91-0.933-0.8870.734-0.283-0.284-0.2830.173-0.303-0.304-0.303-2.773-0.176
Percentage of OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedDefinedBenefitPlansAdjustment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value-2.067-2.066-2.843-0.504-0.504-0.5042.8952.8012.8012.801-1.143-0.91-0.933-0.8870.734-0.283-0.284-0.2830.173-0.303-0.304-0.303-2.773
Percentage of OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent

us-gaap:OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent


None
Period End2020-06-302019-06-30
Value10338
Percentage of OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent100.0100.0

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1367000.0601000.0255000.0-1380000.0-3740000.0868000.0185000.0936000.01564000.033000.0657000.0988000.01068000.0690000.0184000.01398000.0113000.0460000.0-31000.096000.01855000.0165000.01671000.0958000.0
Percentage of OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value107-78.1533.224153542-5.58-1.416-15.068-34.754-7.1912.2127.7885.479-36.3062.8242124-20.633-7.334-21.2029.372-1.565-7.793
Percentage of OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax us-gaap:StatementEquityComponents

us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value105-78.7542.969163941-5.765-2.352-16.632-34.787-7.8481.2246.724.789-36.491.4262124-20.602-7.43-23.0579.207-3.236
Percentage of OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax98.7100.892.1108.9110.698.0103.3166.1110.4100.1109.155.386.387.4100.550.599.598.199.8101.3108.798.2206.8

us-gaap:OtherCostAndExpenseOperating

us-gaap:OtherCostAndExpenseOperating


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value291927252526212424233222262528231923201818202020
Percentage of OtherCostAndExpenseOperating100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherCostAndExpenseOperating us-gaap:ConsolidationItems

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value291927252526212424233222262528231923201818202020
Percentage of OtherCostAndExpenseOperating100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherCostAndExpenseOperating us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value4.7944.0694.7084.7724.4913.0850.00.00.0
Percentage of OtherCostAndExpenseOperating16.420.517.218.517.711.80.00.00.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value126.867108.5969.3747.5086.8438.7199.0857.9353.4338.7149.814108.8087.5265.9279.596.8577.2545.4346.1787.057.045
Percentage of OtherCostAndExpenseOperating43.634.637.433.337.028.831.836.336.633.610.438.637.340.131.331.930.541.133.239.228.930.135.034.4

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value5.6434.2955.9395.2975.0174.1235.3635.2155.0065.1474.8674.0865.1574.7326.9944.8473.3233.5753.222.3973.4423.7152.9622.314
Percentage of OtherCostAndExpenseOperating19.421.721.720.519.815.824.921.720.221.814.818.119.618.924.920.517.115.315.613.018.318.114.711.3

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value4.5173.0965.1695.4934.5214.2643.6024.9825.6285.381175.6617.2075.9788.0666.6915.655.5265.6433.9295.2125.9225.2826.307
Percentage of OtherCostAndExpenseOperating15.515.618.921.317.816.416.820.722.722.853.125.127.423.828.728.429.123.727.321.327.728.926.230.8

us-gaap:OperatingSegments, us-gaap:AllOtherSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1.4851.4951.3251.6551.9317.0695.6945.1215.0765.177.1764.1354.1654.3224.2744.5314.5034.6164.9284.9024.7144.6954.8434.785
Percentage of OtherCostAndExpenseOperating5.17.54.86.47.627.126.521.320.521.921.818.315.817.215.219.223.219.823.926.525.122.924.123.4

us-gaap:OtherNoncashIncome

us-gaap:OtherNoncashIncome


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value7.5777.457.3018.6338.9268.0498.7099.291108.9888.3791011129.873235.9865.7967.1915.04.4083.8943.382
Percentage of OtherNoncashIncome100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherOperatingIncome us-gaap:InvestmentType

us-gaap:OtherOperatingIncome

us-gaap:RealEstate


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value800000.0700000.0800000.0700000.0800000.0600000.0500000.0600000.0600000.0500000.0800000.0700000.0700000.0700000.0600000.0700000.0
Percentage of OtherOperatingIncome100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherThanTemporaryImpairmentLossDebtSecuritiesPortionRecognizedInEarnings

us-gaap:OtherThanTemporaryImpairmentLossDebtSecuritiesPortionRecognizedInEarnings


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-30
Value001945000.05902000.0000000
Percentage of OtherThanTemporaryImpairmentLossDebtSecuritiesPortionRecognizedInEarnings0.00.0100.0100.00.00.00.00.00.00.0

us-gaap:OtherThanTemporaryImpairmentLossDebtSecuritiesPortionRecognizedInEarnings us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:StatementEquityComponents

us-gaap:ReclassificationOutOfAccumulatedOtherComprehensiveIncome, us-gaap:AccumulatedNetUnrealizedInvestmentGainLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value0001945000.05902000.000000112000.000
Percentage of OtherThanTemporaryImpairmentLossDebtSecuritiesPortionRecognizedInEarnings0.00.00.0100.0100.00.00.00.00.00.00.00.00.0

us-gaap:OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent

us-gaap:OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-2000.0-2000.016000.0-2000.0-2000.0-3000.021000.0-3000.0-3000.0-3000.0530000.026000.023000.020000.030000.027000.027000.026000.02504000.0284000.0105000.0160000.0129000.00
Percentage of OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0

us-gaap:OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentHeldtomaturitySecurities us-gaap:StatementEquityComponents

us-gaap:OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentHeldtomaturitySecurities

us-gaap:AccumulatedOtherThanTemporaryImpairment


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value0000000000-631000.00000000-2013000.00000
Percentage of OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentHeldtomaturitySecurities0.00.00.00.00.00.00.00.00.00.0100.00.00.00.00.00.00.00.0100.00.00.00.00.0

us-gaap:PaymentsForDerivativeInstrumentInvestingActivities

us-gaap:PaymentsForDerivativeInstrumentInvestingActivities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1722192018182318222219191817171819192025211920
Percentage of PaymentsForDerivativeInstrumentInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsForProceedsFromPolicyLoans

us-gaap:PaymentsForProceedsFromPolicyLoans


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value-1225000.0-1972000.0-264000.0117000.0-1007000.0-1690000.0250000.0-1129000.088000.0-890000.0-1061000.0-433000.0130000.0-930000.0-519000.0-1369000.099000.0-1469000.0346000.0-322000.0-1944000.0232000.0-101000.0
Percentage of PaymentsForProceedsFromPolicyLoans100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsToAcquireAvailableForSaleSecuritiesDebt

us-gaap:PaymentsToAcquireAvailableForSaleSecuritiesDebt


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value1692595056203666341269975
Percentage of PaymentsToAcquireAvailableForSaleSecuritiesDebt100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsToAcquireBusinessesNetOfCashAcquired

us-gaap:PaymentsToAcquireBusinessesNetOfCashAcquired


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value0.00.00.00.00.0011890.00.00.00.0
Percentage of PaymentsToAcquireBusinessesNetOfCashAcquired0.00.00.00.0100.0100.00.00.00.00.0

us-gaap:PaymentsToAcquireHeldToMaturitySecurities

us-gaap:PaymentsToAcquireHeldToMaturitySecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value937596578320804820014219281792171514610975125150262271-160.254
Percentage of PaymentsToAcquireHeldToMaturitySecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsToAcquireMortgageNotesReceivable

us-gaap:PaymentsToAcquireMortgageNotesReceivable


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value3.3636.996731415175.081149.8710.024216.387238.32328172315333.4080.3511.2813.119
Percentage of PaymentsToAcquireMortgageNotesReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsToAcquireOtherInvestments

us-gaap:PaymentsToAcquireOtherInvestments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1.1110.001-4.6395.0456.9082.7334.9950.490.0960.0020.1410.1880.01.984.2941.714212.910.92-0.0010.4210.0
Percentage of PaymentsToAcquireOtherInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.00.0

us-gaap:PresentValueOfFutureInsuranceProfitsAmortizationExpense1

us-gaap:PresentValueOfFutureInsuranceProfitsAmortizationExpense1


None
Period End2020-06-302020-03-31
Value1609000.02192000.0
Percentage of PresentValueOfFutureInsuranceProfitsAmortizationExpense1100.0100.0

us-gaap:ProceedsFromAnnuitiesAndInvestmentCertificates

us-gaap:ProceedsFromAnnuitiesAndInvestmentCertificates


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1051171121059592117125161154181186179181221196235194239227249202269
Percentage of ProceedsFromAnnuitiesAndInvestmentCertificates100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromDerivativeInstrumentInvestingActivities

us-gaap:ProceedsFromDerivativeInstrumentInvestingActivities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1452247.052183.04730544659685051488.575110.02.091619382639
Percentage of ProceedsFromDerivativeInstrumentInvestingActivities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromLinesOfCredit

us-gaap:ProceedsFromLinesOfCredit


None
Period End2020-06-302020-03-312019-06-302019-03-31
Value0.00.00.075
Percentage of ProceedsFromLinesOfCredit0.00.00.0100.0

us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities

us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value63931055282552762987.1566577747057352672505611448116
Percentage of ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities

us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1871872141751721377784162113187691121201001151345413186155101-145.857
Percentage of ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromSaleAndCollectionOfMortgageNotesReceivable

us-gaap:ProceedsFromSaleAndCollectionOfMortgageNotesReceivable


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value1.8222.149250.1327.081152.78510183.3651.7021.5143.686181.1741.0412.9131347126.9076.394
Percentage of ProceedsFromSaleAndCollectionOfMortgageNotesReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromSaleAndMaturityOfOtherInvestments

us-gaap:ProceedsFromSaleAndMaturityOfOtherInvestments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value0.1689.5650.4740.88721133.7110.5292.220.04.3884.9430.00.00.0940.2351.9091.8031.5022.1820.00.00.152
Percentage of ProceedsFromSaleAndMaturityOfOtherInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.00.00.0100.0100.0100.0100.0100.0100.00.00.0100.0

us-gaap:ProceedsFromSaleOfAvailableForSaleSecuritiesDebt

us-gaap:ProceedsFromSaleOfAvailableForSaleSecuritiesDebt


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value0.00.06.770.07.2717315130.00.00.00.0
Percentage of ProceedsFromSaleOfAvailableForSaleSecuritiesDebt0.00.0100.00.0100.0100.0100.0100.00.00.00.00.0

us-gaap:ProceedsFromStockOptionsExercised

us-gaap:ProceedsFromStockOptionsExercised


None
Period End2020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302016-12-312016-03-312015-12-312015-03-312014-12-31
Value0000000-600000.0400000.0-300000.00000
Percentage of ProceedsFromStockOptionsExercised0.00.00.00.00.00.00.0100.0100.0100.00.00.00.00.0

us-gaap:ProvisionForLoanAndLeaseLosses

us-gaap:ProvisionForLoanAndLeaseLosses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value342000.0706000.0000025000.00000000000000000
Percentage of ProvisionForLoanAndLeaseLosses100.0100.00.00.00.00.0100.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RepaymentsOfAnnuitiesAndInvestmentCertificates

us-gaap:RepaymentsOfAnnuitiesAndInvestmentCertificates


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value246262242247250248251246249252205208246231224206234234242222218227225
Percentage of RepaymentsOfAnnuitiesAndInvestmentCertificates100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RepaymentsOfLinesOfCredit

us-gaap:RepaymentsOfLinesOfCredit


None
Period End2020-06-302020-03-312019-06-302019-03-31
Value0.00.00.075
Percentage of RepaymentsOfLinesOfCredit0.00.00.0100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareBasedLiabilitiesPaid

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareBasedLiabilitiesPaid


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value01900000.0600000.0002500000.02500000.0300000.0400000.01500000.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareBasedLiabilitiesPaid0.0100.0100.00.00.0100.0100.0100.0100.0100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value-0.00030.0021-0.0001-0.000100.00140.0001-0.000100.00120.0001-0.0001-0.00010.0012-0.000600.00020.0016-0.00020.000200.00140
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate100.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.00.0100.00.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate us-gaap:Range

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate

srt:WeightedAverage


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
Value-0.00030.0023-0.0009-0.0017-0.00480.0235-0.00050.0019
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate us-gaap:Range

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate

srt:WeightedAverage


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
Value0.03420.2830.0026-0.0009-0.00150.22170.0059-0.0012
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised

us-gaap:PerformanceShares


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value101.04049.00005426.0000000000000
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised100.0100.00.00.00.0100.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:RestrictedStockUnitsRSU


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value51.02306.01980.0003051.01630.0001494.0002563.000000
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised50.557.00.00.00.056.20.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:StockAppreciationRightsSARS


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value01372.0928.000011050.01656.0353.0975.03490.0134.01006.0722.018268.0900.0100.0275.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised0.033.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeitures us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeitures

us-gaap:PerformanceShares


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value00399.00215.0401.00000110.0000301.0000
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeitures0.00.0100.00.0100.0100.00.00.00.00.0100.00.00.00.0100.00.00.00.0

us-gaap:RestrictedStockUnitsRSU


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value00255.00107.0200.00137.094.0325.0138.0166.072.0089.061.045.00
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeitures0.00.063.90.049.849.90.00.00.00.0125.50.00.00.029.60.00.00.0

us-gaap:StockAppreciationRightsSARS


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value120.0872.0148.067.0620.0543.00338.0535.0907.0943.0400.0001357.01844.0982.00
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeitures0.00.037.10.0288.4135.40.00.00.00.0857.30.00.00.0450.80.00.00.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted

us-gaap:PerformanceShares


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-02-172016-03-31
Value006427.00005070.00004210.00101.04425.00005727.05727.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted0.00.0100.00.00.00.0100.00.00.00.0100.00.0100.0100.00.00.00.0100.0100.0

us-gaap:RestrictedStockUnitsRSU


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-04-142016-06-302016-02-172016-03-31
Value006775.00005129.00004246.0051.04334.0002563.02563.03661.03661.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted0.00.0105.40.00.00.0101.20.00.00.0100.90.050.597.90.00.00.00.063.963.9

us-gaap:StockAppreciationRightsSARS


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-02-172016-03-31
Value0020380.000012590.000010469.00203.011512.000014643.014643.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted0.00.0317.10.00.00.0248.30.00.00.0248.70.0201.0260.20.00.00.0255.7255.7

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value01900000.0600000.0002500000.02500000.0300000.0400000.01500000.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue0.0100.0100.00.00.0100.0100.0100.0100.0100.0

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage us-gaap:AwardType

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage

us-gaap:RestrictedStockUnitsRSU


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value01.00001.00
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.0100.00.00.00.0100.00.0

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage us-gaap:AwardType, us-gaap:Vesting

nwli:EmployeeStockAppreciationRightsSARs, us-gaap:ShareBasedCompensationAwardTrancheOne


None
Period End2020-06-302020-03-31
Value00.333
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.033.3

nwli:EmployeeStockAppreciationRightsSARs, us-gaap:ShareBasedCompensationAwardTrancheThree


None
Period End2020-06-302020-03-31
Value00.333
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.033.3

nwli:EmployeeStockAppreciationRightsSARs, us-gaap:ShareBasedCompensationAwardTrancheTwo


None
Period End2020-06-302020-03-31
Value00.333
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.033.3

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage us-gaap:TitleOfIndividual, us-gaap:AwardType, us-gaap:Vesting

nwli:Employees, nwli:EmployeeStockAppreciationRightsSARsGrantedBefore2016, nwli:ShareBasedCompensationAwardTrancheFive


None
Period End2020-03-31
Value0.2
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage20.0

nwli:Employees, nwli:EmployeeStockAppreciationRightsSARsGrantedBefore2016, nwli:ShareBasedCompensationAwardTrancheFour


None
Period End2020-03-31
Value0.2
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage20.0

nwli:Employees, nwli:EmployeeStockAppreciationRightsSARsGrantedBefore2016, us-gaap:ShareBasedCompensationAwardTrancheOne


None
Period End2020-06-302020-03-31
Value00.2
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.020.0

nwli:Employees, nwli:EmployeeStockAppreciationRightsSARsGrantedBefore2016, us-gaap:ShareBasedCompensationAwardTrancheThree


None
Period End2020-06-302020-03-31
Value00.2
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.020.0

nwli:Employees, nwli:EmployeeStockAppreciationRightsSARsGrantedBefore2016, us-gaap:ShareBasedCompensationAwardTrancheTwo


None
Period End2020-06-302020-03-31
Value00.2
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.020.0

srt:Director, nwli:EmployeeStockOptionsandStockAppreciationRightsSARs, nwli:ShareBasedCompensationAwardTrancheFive


None
Period End2020-03-31
Value0.2
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage20.0

srt:Director, nwli:EmployeeStockOptionsandStockAppreciationRightsSARs, nwli:ShareBasedCompensationAwardTrancheFour


None
Period End2020-03-31
Value0.2
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage20.0

srt:Director, nwli:EmployeeStockOptionsandStockAppreciationRightsSARs, us-gaap:ShareBasedCompensationAwardTrancheOne


None
Period End2020-06-302020-03-312019-09-30
Value00.20
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.020.00.0

srt:Director, nwli:EmployeeStockOptionsandStockAppreciationRightsSARs, us-gaap:ShareBasedCompensationAwardTrancheThree


None
Period End2020-06-302020-03-31
Value00.2
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.020.0

srt:Director, nwli:EmployeeStockOptionsandStockAppreciationRightsSARs, us-gaap:ShareBasedCompensationAwardTrancheTwo


None
Period End2020-06-302020-03-31
Value00.2
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage0.020.0

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1

us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value01800000.01400000.0100000.0-100000.03000000.02300000.000800000.02100000.0-100000.0200000.0500000.0
Percentage of SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue10.0100.0100.0100.0100.0100.0100.00.00.0100.0100.0100.0100.0100.0

us-gaap:UndistributedEarnings

us-gaap:UndistributedEarnings


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value48-2.06236193340203532263821252322332617301628212827
Percentage of UndistributedEarnings100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:UndistributedEarnings us-gaap:StatementClassOfStock

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value47-2.00435193239193431263721242221322516291528202726
Percentage of UndistributedEarnings97.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.297.2

us-gaap:CommonClassB


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1.369-0.0581.0310.5650.9531.1370.581.0080.9180.761.0840.6170.7210.6660.6320.9540.7430.4880.8690.4580.8160.6030.7950.769
Percentage of UndistributedEarnings2.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.82.8

us-gaap:UnrealizedGainLossOnDerivatives

us-gaap:UnrealizedGainLossOnDerivatives


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value40-106.629603.2971742-115.5856910-44.3948445326120192.095-12.9018.134-52.815-8.782-8.28719
Percentage of UnrealizedGainLossOnDerivatives100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:WeightedAverageNumberDilutedSharesOutstandingAdjustment us-gaap:StatementClassOfStock

us-gaap:WeightedAverageNumberDilutedSharesOutstandingAdjustment

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-30
Value00000000004000.0001000.01000.01000.02000.02000.0
Percentage of WeightedAverageNumberDilutedSharesOutstandingAdjustment0.00.00.00.00.00.00.00.00.00.0100.00.00.0100.0100.0100.0100.0100.0

dei:EntityCommonStockSharesOutstanding us-gaap:StatementClassOfStock

dei:EntityCommonStockSharesOutstanding

us-gaap:CommonClassA


None
Period End2020-08-062020-05-082020-02-282019-11-062019-08-072019-05-092019-02-282018-11-062018-08-062018-05-082018-02-282017-11-022017-08-032017-05-082017-03-102016-11-032016-08-042016-05-052016-03-102015-11-05
Value3436000.03436000.03436000.03436000.03436000.03436000.03436000.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.03436200.0
Percentage of EntityCommonStockSharesOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses

nwli:DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses


None
Period End2020-06-302020-03-312019-12-31
Value689869907106
Percentage of DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses100.0100.0100.0

nwli:DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses nwli:CreditRating

nwli:AAARating


None
Period End2020-06-302020-03-31
Value9397
Percentage of DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses1.41.4

nwli:AARating


None
Period End2020-06-302020-03-31
Value17391853
Percentage of DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses25.226.5

nwli:ARating


None
Period End2020-06-302020-03-31
Value22332212
Percentage of DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses32.431.7

nwli:BBBRating


None
Period End2020-06-302020-03-31
Value27302753
Percentage of DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses39.639.4

nwli:BBRatingAndBelow


None
Period End2020-06-302020-03-31
Value10272
Percentage of DebtSecuritiesHeldToMaturityNetOfAllowanceForCreditLosses1.51.0

nwli:DeferredPolicyAcquisitionCostsSalesInducementsAndValueOfBusinessAcquired us-gaap:ConsolidationItems

nwli:DeferredPolicyAcquisitionCostsSalesInducementsAndValueOfBusinessAcquired

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-31
Value908103296698510081063975955
Percentage of DeferredPolicyAcquisitionCostsSalesInducementsAndValueOfBusinessAcquired100.0100.0100.0100.0100.0100.0100.0100.0

nwli:DeferredPolicyAcquisitionCostsSalesInducementsAndValueOfBusinessAcquired us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value1401411421421431460.0
Percentage of DeferredPolicyAcquisitionCostsSalesInducementsAndValueOfBusinessAcquired15.513.714.714.514.213.80.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-31
Value444533486501528567609603
Percentage of DeferredPolicyAcquisitionCostsSalesInducementsAndValueOfBusinessAcquired48.951.750.350.952.453.462.563.2

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-31
Value130140127123119118122101
Percentage of DeferredPolicyAcquisitionCostsSalesInducementsAndValueOfBusinessAcquired14.413.613.212.511.911.112.610.6

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-31
Value192217209217217231243250
Percentage of DeferredPolicyAcquisitionCostsSalesInducementsAndValueOfBusinessAcquired21.221.121.722.121.521.725.026.2

nwli:FairValueInvestmentsPercentOfTotal us-gaap:FairValueByFairValueHierarchyLevel

nwli:FairValueInvestmentsPercentOfTotal

us-gaap:FairValueInputsLevel1


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value0.0050.0050.0070.0060.0060.0060.0060.0060.0060.0060.0060.0060.0060.0060.0060.0060.0060.0060.0060.0060.006
Percentage of FairValueInvestmentsPercentOfTotal100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueInputsLevel2


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value0.9760.9870.9480.9640.9680.9730.9890.950.9610.9580.9340.9430.9470.9470.9560.9660.9730.980.9810.9850.954
Percentage of FairValueInvestmentsPercentOfTotal19520.019740.013542.916066.716133.316216.716483.315833.316016.715966.715566.715716.715783.315783.315933.316100.016216.716333.316350.016416.715900.0

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value0.0190.0080.0450.030.0260.0210.0050.0440.0330.0360.060.0510.0470.0470.0380.0280.0210.0140.0130.0090.04
Percentage of FairValueInvestmentsPercentOfTotal380.0160.0642.9500.0433.3350.083.3733.3550.0600.01000.0850.0783.3783.3633.3466.7350.0233.3216.7150.0666.7

nwli:InterestInTrustFairValueDisclosure us-gaap:FairValueByMeasurementBasis

nwli:InterestInTrustFairValueDisclosure

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value9.239.239.238.6928.6928.6928.6928.6768.6768.6768.6767.557.557.557.557.3797.3797.3797.3790.00.0
Percentage of InterestInTrustFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.0

nwli:LiabilityForDeferredAnnuityContractsFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

nwli:LiabilityForDeferredAnnuityContractsFairValueDisclosure

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value551157605916582760096207640371277188725273387418737073927367731472857265728872217178
Percentage of LiabilityForDeferredAnnuityContractsFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:LiabilityForDeferredAnnuityContractsFairValueDisclosure us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value675568666999708772097337745576117684775878657806775177717739769376567626764076097546
Percentage of LiabilityForDeferredAnnuityContractsFairValueDisclosure122.6119.2118.3121.6120.0118.2116.4106.8106.9107.0107.2105.2105.2105.1105.0105.2105.1105.0104.8105.4105.1

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value551157605916582760096207640371277188725273387418737073927367731472857265728872217178
Percentage of LiabilityForDeferredAnnuityContractsFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContractsFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

nwli:LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContractsFairValueDisclosure

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value455449422432426419415417427430443469474470470485488482461472474
Percentage of LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContractsFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContractsFairValueDisclosure us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value403399400405404405407415422423430439443442443443444445434440446
Percentage of LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContractsFairValueDisclosure88.688.994.793.794.896.798.099.798.898.397.193.693.594.094.291.291.092.294.293.294.0

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value455449422432426419415417427430443469474470470485488482461472474
Percentage of LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContractsFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:LiabilityForFuturePolicyBenefitsUniversalLifeAndAnnuityContracts

nwli:LiabilityForFuturePolicyBenefitsUniversalLifeAndAnnuityContracts


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value904091259288932994209524960897999818985599629856978197749722966196229565956195049384
Percentage of LiabilityForFuturePolicyBenefitsUniversalLifeAndAnnuityContracts100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:LoansGrossInsurancePolicyFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

nwli:LoansGrossInsurancePolicyFairValueDisclosure

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value13213512312712211990879294100102104102101113116112108111111
Percentage of LoansGrossInsurancePolicyFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:LoansGrossInsurancePolicyFairValueDisclosure us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value767880808081545455555657575758596060616163
Percentage of LoansGrossInsurancePolicyFairValueDisclosure58.157.464.762.865.467.960.362.160.159.056.356.055.756.458.152.352.053.657.155.257.3

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value13213512312712211990879294100102104102101113116112108111111
Percentage of LoansGrossInsurancePolicyFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:MortgageLoansOnRealEstateAllowanceForPossibleLossPercentage us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable

nwli:MortgageLoansOnRealEstateAllowanceForPossibleLossPercentage

us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-31
Value0.0080.0070.002
Percentage of MortgageLoansOnRealEstateAllowanceForPossibleLossPercentage100.0100.0100.0

nwli:MortgageLoansOnRealEstateByLoansToValueRatioPercentage us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable

nwli:MortgageLoansOnRealEstateByLoansToValueRatioPercentage

us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-31
Value0.9920.9930.998
Percentage of MortgageLoansOnRealEstateByLoansToValueRatioPercentage100.0100.0100.0

nwli:MortgageLoansOnRealEstateCommercialAndConsumerNetFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

nwli:MortgageLoansOnRealEstateCommercialAndConsumerNetFairValueDisclosure

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value27227827022722520520220019720520818918416417615013411311192156
Percentage of MortgageLoansOnRealEstateCommercialAndConsumerNetFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:MortgageLoansOnRealEstateCommercialAndConsumerNetFairValueDisclosure us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value27327627222421420520320019620420818818316317414613011010888149
Percentage of MortgageLoansOnRealEstateCommercialAndConsumerNetFairValueDisclosure100.599.3100.698.694.999.9100.2100.199.799.799.799.499.599.498.797.997.497.497.495.395.5

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value27227827022722520520220019720520818918416417615013411311192156
Percentage of MortgageLoansOnRealEstateCommercialAndConsumerNetFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

nwli:MortgageLoansOnRealEstatePercentageOfTotalPercentage nwli:MortgageLoansByLoanToValueRatio, us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable

nwli:MortgageLoansOnRealEstatePercentageOfTotalPercentage

nwli:MortgageLoansByLoansToValueRatioFiftyToSixtyPercent, us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-31
Value0.1820.1650.208
Percentage of MortgageLoansOnRealEstatePercentageOfTotalPercentage100.0100.0100.0

nwli:MortgageLoansByLoansToValueRatioLessThanFiftyPercent, us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-31
Value0.1920.2060.193
Percentage of MortgageLoansOnRealEstatePercentageOfTotalPercentage105.5124.892.8

nwli:MortgageLoansByLoansToValueRatioSeventyToEightyPercent, us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-31
Value0.1660.1690.169
Percentage of MortgageLoansOnRealEstatePercentageOfTotalPercentage91.2102.481.3

nwli:MortgageLoansByLoansToValueRatioSixtyToSeventyPercent, us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-31
Value0.460.460.43
Percentage of MortgageLoansOnRealEstatePercentageOfTotalPercentage252.7278.8206.7

nwli:OtherAssetsBookValueAndFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

nwli:OtherAssetsBookValueAndFairValueDisclosure

us-gaap:FairValueInputsLevel1


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value0.0020.0020.0020.0
Percentage of OtherAssetsBookValueAndFairValueDisclosure100.0100.0100.00.0

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value22221614
Percentage of OtherAssetsBookValueAndFairValueDisclosure1129000.01129000.0809000.00.0

nwli:OtherAssetsBookValueAndFairValueDisclosure us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value4.5154.5150.1970.195
Percentage of OtherAssetsBookValueAndFairValueDisclosure225750.0225750.09850.00.0

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value22221614
Percentage of OtherAssetsBookValueAndFairValueDisclosure1129100.01129100.0809100.00.0

nwli:PolicyholderAccountBalancesFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:ValuationTechnique

nwli:PolicyholderAccountBalancesFairValueDisclosure

us-gaap:FairValueInputsLevel3, nwli:DeterministicCashFlow


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value876115544
Percentage of PolicyholderAccountBalancesFairValueDisclosure100.0100.0100.0100.0

nwli:PolicyholderAccountsBalancesMeasurementInput us-gaap:Range, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique

nwli:PolicyholderAccountsBalancesMeasurementInput

srt:Maximum, us-gaap:FairValueInputsLevel3, nwli:MeasurementInputProjectedOptionCost, nwli:DeterministicCashFlow


None
Period End2020-06-302020-03-312019-12-31
Value0.31120.15950.1755
Percentage of PolicyholderAccountsBalancesMeasurementInput100.0100.0100.0

srt:WeightedAverage, us-gaap:FairValueInputsLevel3, nwli:MeasurementInputProjectedOptionCost, nwli:DeterministicCashFlow


None
Period End2020-06-302020-03-312019-12-31
Value0.04560.01320.0314
Percentage of PolicyholderAccountsBalancesMeasurementInput14.78.317.9

nwli:RealEstateFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

nwli:RealEstateFairValueDisclosure

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value48485753
Percentage of RealEstateFairValueDisclosure100.0100.0100.0100.0

nwli:RealEstateFairValueDisclosure us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value34343435
Percentage of RealEstateFairValueDisclosure70.670.960.566.7

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value48485753
Percentage of RealEstateFairValueDisclosure100.0100.0100.0100.0

nwli:ShareBasedCompensationFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:ValuationTechnique

nwli:ShareBasedCompensationFairValueDisclosure

us-gaap:FairValueInputsLevel3, nwli:BlackScholes


None
Period End2020-06-302020-03-312019-12-31
Value5.4973.08111
Percentage of ShareBasedCompensationFairValueDisclosure100.0100.0100.0

nwli:ShareBasedCompensationMeasurementInput us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique

nwli:ShareBasedCompensationMeasurementInput

us-gaap:FairValueInputsLevel3, nwli:MeasurementInputExpectedVolatility, nwli:BlackScholes


None
Period End2020-06-302020-03-312019-12-31
Value0.31720.2830.222
Percentage of ShareBasedCompensationMeasurementInput100.0100.0100.0

nwli:ShareBasedCompensationMeasurementInput us-gaap:Range, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique

srt:Maximum, us-gaap:FairValueInputsLevel3, us-gaap:MeasurementInputExpectedTerm, nwli:BlackScholes


None
Period End2020-06-302020-03-312019-12-31
Value9.49.710.0
Percentage of ShareBasedCompensationMeasurementInput2963.43427.64504.5

srt:Minimum, us-gaap:FairValueInputsLevel3, us-gaap:MeasurementInputExpectedTerm, nwli:BlackScholes


None
Period End2020-06-302020-03-312019-12-31
Value1.51.71.9
Percentage of ShareBasedCompensationMeasurementInput472.9600.7855.9

us-gaap:AccruedIncomeTaxes

us-gaap:AccruedIncomeTaxes


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302015-12-312015-09-302014-12-31
Value1.4580.03.7481.2820.02.0050.00.02.7010.00.0180.7899.1499.9380.00.03.336
Percentage of AccruedIncomeTaxes100.00.0100.0100.00.0100.00.00.0100.00.00.0100.0100.0100.0100.00.00.0100.0

us-gaap:AccruedInvestmentIncomeReceivable

us-gaap:AccruedInvestmentIncomeReceivable


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value9195939898105961019899961039810199101981029910096
Percentage of AccruedInvestmentIncomeReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AllowanceForLoanAndLeaseLossesRealEstate

us-gaap:AllowanceForLoanAndLeaseLossesRealEstate


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value2227000.01885000.0675000.0675000.0675000.0675000.0675000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0650000.0
Percentage of AllowanceForLoanAndLeaseLossesRealEstate100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AllowanceForLoanAndLeaseLossesRealEstate us-gaap:CumulativeEffectPeriodOfAdoption

srt:CumulativeEffectPeriodOfAdoptionAdjustment


None
Period End2020-03-312019-12-312019-03-312018-12-31
Value0504000.000
Percentage of AllowanceForLoanAndLeaseLossesRealEstate0.074.70.00.0

us-gaap:AllowanceForLoanAndLeaseLossesRealEstate us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable

us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-31
Value2227000.01885000.0675000.0
Percentage of AllowanceForLoanAndLeaseLossesRealEstate100.0100.0100.0

us-gaap:AssetsFairValueDisclosure

us-gaap:AssetsFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value345732143538353534843424297831213100321932543209319231893181319630932966291728852842
Percentage of AssetsFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AssetsFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:FairValueInputsLevel1


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value171523191919171918181819191918181918171716
Percentage of AssetsFairValueDisclosure0.50.50.70.60.60.60.60.60.60.60.60.60.60.60.60.60.60.60.60.60.6

us-gaap:FairValueInputsLevel2


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value337331743356340933753334294629652980308430413025302330203042308730112906286128422711
Percentage of AssetsFairValueDisclosure97.698.794.996.496.997.498.995.096.195.893.494.394.794.795.696.697.398.098.198.595.4

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value66241571068971141361021161941631491491209063423825114
Percentage of AssetsFairValueDisclosure1.90.84.53.02.62.10.54.43.33.66.05.14.74.73.82.82.01.41.30.94.0

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value234761531491155117192487106105928717217012682107143
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value1.3410.3021.3972.3472.2720.8250.193
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax0.60.40.91.62.01.61.1

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value0.6130.0031.0711.3751.010.485
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax0.30.00.70.90.90.9

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value21865141133102441517223681
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax93.386.192.489.889.187.387.588.288.60.093.5

us-gaap:ForeignGovernmentDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.3120.1520.2030.2440.2520.1940.030.0360.0110.0880.326
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax0.10.20.10.20.20.40.20.20.00.00.4

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value4.9152.3633.4763.9143.3492.0951.0451.1191.5533.64
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax2.13.12.32.62.94.15.95.86.24.2

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value1.3191.341.0771.2131.211.0250.9370.8360.9651.1911.376
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax0.61.80.70.81.02.05.34.33.90.01.6

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value7.1926.4774.4956.1784.5431.8640.00.0050.00.00.0
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax3.18.52.94.13.93.60.00.00.00.00.0

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value271082.5995.4525.86623806766108.1941016225.6528.5382655349.132
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value0.6612.4590.00.00.00.0630.0
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax2.42.30.00.00.00.30.0

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value0.3191.1830.00.00.00.0
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax1.21.10.00.00.00.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value261042.4795.3435.764237966664310
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax95.896.195.498.098.398.699.299.099.20.099.3

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.00.4060.00.00.00.1480.5170.6090.4510.0
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax0.00.40.00.00.00.60.60.90.70.0

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.1590.1920.1170.1070.1010.120.0840.0590.0470.0360.052
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax0.60.24.52.01.70.50.10.10.10.00.5

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.0050.0080.0030.0020.0010.00.0040.00.0050.0250.029
Percentage of AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax0.00.00.10.00.00.00.00.00.00.00.3

us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis

us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value316632063206326532653306300830133022308729642927292829432977292028482806283327692577
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value5861677581905.969
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis1.81.92.12.32.52.70.2

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value272728282833
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis0.90.90.90.90.91.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value29052941292129602950297728932895290029672842
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis91.891.791.190.690.490.096.296.196.096.195.9

us-gaap:ForeignGovernmentDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value9.9889.9869.9839.9819.9789.9769.9749.9719.9699.9679.964
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis0.30.30.30.30.30.30.30.30.30.30.3

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value64646776788082848683
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis2.02.02.12.42.42.42.82.82.92.8

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value1112121314151516171920
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis0.40.40.40.40.40.50.50.60.60.60.7

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value8989981001001000.570.5710.5720.5740.575
Percentage of AvailableForSaleDebtSecuritiesAmortizedCostBasis2.82.83.13.13.13.00.00.00.00.00.0

us-gaap:AvailableForSaleSecuritiesDebtSecurities

us-gaap:AvailableForSaleSecuritiesDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value337331743356340933753334294629652980308430413025302330203042308730112905286128422711
Percentage of AvailableForSaleSecuritiesDebtSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtSecurities nwli:PricingSource

nwli:PricedByThirdPartyVendors


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value33733174335634093375333429462965298030843041
Percentage of AvailableForSaleSecuritiesDebtSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtSecurities nwli:PricingSource, us-gaap:FairValueByFairValueHierarchyLevel

nwli:PricedByThirdPartyVendors, us-gaap:FairValueInputsLevel2


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value33733174335634093375333429462965298030843041
Percentage of AvailableForSaleSecuritiesDebtSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtSecurities us-gaap:BusinessAcquisition

nwli:OzarkNationalLifeInsuranceCompany


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value408388415428403392
Percentage of AvailableForSaleSecuritiesDebtSecurities12.112.212.412.612.011.8

us-gaap:AvailableForSaleSecuritiesDebtSecurities us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:FairValueInputsLevel2


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value33733174335634093375333429462965298030843041
Percentage of AvailableForSaleSecuritiesDebtSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtSecurities us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value3373317433563409337533342946296529803084
Percentage of AvailableForSaleSecuritiesDebtSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value3373317433563409337533342946296529803084
Percentage of AvailableForSaleSecuritiesDebtSecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AvailableForSaleSecuritiesDebtSecurities us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value5959687784906.162
Percentage of AvailableForSaleSecuritiesDebtSecurities1.81.92.02.32.52.70.2

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value272629302933
Percentage of AvailableForSaleSecuritiesDebtSecurities0.80.80.90.90.91.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value30972903306030883047299828292845285629602913
Percentage of AvailableForSaleSecuritiesDebtSecurities91.891.591.290.690.389.996.095.995.896.095.8

us-gaap:ForeignGovernmentDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value10101010101010109.981010
Percentage of AvailableForSaleSecuritiesDebtSecurities0.30.30.30.30.30.30.30.30.30.30.3

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value69667180828283858787
Percentage of AvailableForSaleSecuritiesDebtSecurities2.12.12.12.42.42.52.82.92.92.9

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value1213131415161617182021
Percentage of AvailableForSaleSecuritiesDebtSecurities0.40.40.40.40.50.50.60.60.60.70.7

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value96951021061051020.5660.5760.5670.5490.546
Percentage of AvailableForSaleSecuritiesDebtSecurities2.93.03.13.13.13.10.00.00.00.00.0

us-gaap:BusinessCombinationContingentConsiderationLiability

us-gaap:BusinessCombinationContingentConsiderationLiability


None
Period End2020-03-31
Value4200000.0
Percentage of BusinessCombinationContingentConsiderationLiability100.0

us-gaap:BusinessCombinationContingentConsiderationLiability us-gaap:BusinessAcquisition

nwli:OzarkNationalLifeInsuranceCompany


None
Period End2020-03-312019-12-312019-09-302019-06-302019-01-31
Value4200000.04100000.04000000.03900000.03700000.0
Percentage of BusinessCombinationContingentConsiderationLiability100.00.00.00.00.0

us-gaap:BusinessCombinationContingentConsiderationLiability us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value04174000.04076000.03965000.03871000.03700000.0
Percentage of BusinessCombinationContingentConsiderationLiability0.099.40.00.00.00.0

us-gaap:BusinessCombinationContingentConsiderationLiability us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:ValuationTechnique

us-gaap:FairValueInputsLevel3, nwli:ValuationProbabilisticMethod


None
Period End2020-03-312019-12-31
Value4174000.04076000.0
Percentage of BusinessCombinationContingentConsiderationLiability99.40.0

us-gaap:BusinessCombinationContingentConsiderationLiability us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value04174000.04076000.03965000.03871000.03700000.0
Percentage of BusinessCombinationContingentConsiderationLiability0.099.40.00.00.00.0

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value04174000.04076000.03965000.03871000.03700000.0
Percentage of BusinessCombinationContingentConsiderationLiability0.099.40.00.00.00.0

us-gaap:BusinessCombinationContingentConsiderationLiabilityMeasurementInput us-gaap:Range, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique

us-gaap:BusinessCombinationContingentConsiderationLiabilityMeasurementInput

srt:WeightedAverage, us-gaap:FairValueInputsLevel3, nwli:MeasurementInputProjectedRenewalPremium, nwli:ValuationProbabilisticMethod


None
Period End2020-03-312019-12-31
Value71-71.9
Percentage of BusinessCombinationContingentConsiderationLiabilityMeasurementInput100.0100.0

us-gaap:CashAndCashEquivalentsFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:CashAndCashEquivalentsFairValueDisclosure

us-gaap:FairValueInputsLevel1


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value450352253171140911311551268221717010987511779314110686277
Percentage of CashAndCashEquivalentsFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CashAndCashEquivalentsFairValueDisclosure us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value450352253171140911311551268221717010987511779314110686277
Percentage of CashAndCashEquivalentsFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value450352253171140911311551268221717010987511779314110686277
Percentage of CashAndCashEquivalentsFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CashCashEquivalentsAndShortTermInvestments

us-gaap:CashCashEquivalentsAndShortTermInvestments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-312012-12-31
Value4503522531711409113115512682217170109875117793141106867171277121120124
Percentage of CashCashEquivalentsAndShortTermInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommonStockValueOutstanding us-gaap:StatementClassOfStock

us-gaap:CommonStockValueOutstanding

us-gaap:CommonClassA


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value34000.034000.034000.034000.034000.034000.034000.034000.034000.034000.034000.034000.034000.034000.034000.034000.034000.034000.034000.03436000.03436000.0
Percentage of CommonStockValueOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommonClassB


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value2000.02000.02000.02000.02000.02000.02000.02000.02000.02000.02000.02000.02000.02000.02000.02000.02000.02000.02000.0200000.0200000.0
Percentage of CommonStockValueOutstanding5.95.95.95.95.95.95.95.95.95.95.95.95.95.95.95.95.95.95.95.85.8

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value29272928189838443358305
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger us-gaap:FinancialInstrument

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value28262827189827442357304
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger96.497.997.697.299.698.799.899.799.7

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-312018-09-302018-06-30
Value0.00.00.09.8440.00.00.0
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger0.00.00.01.20.00.00.0

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.5940.5770.710.7980.8450.8410.8780.9330.979
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger2.02.12.42.80.40.10.20.30.3

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-30
Value0.4640.00.00.00.00.00.00.0
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger1.60.00.00.00.00.00.00.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value2.8664.4582.4915.3115.83221352421
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss us-gaap:FinancialInstrument

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value2.7064.2662.3745.2045.73121352421
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss94.495.795.398.098.398.899.899.899.8

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-312018-09-302018-06-30
Value0.00.00.00.1480.00.00.0
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss0.00.00.00.70.00.00.0

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.1590.1920.1170.1070.1010.120.0840.0590.047
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss5.54.34.72.01.70.60.20.20.2

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-30
Value0.0010.00.00.00.00.00.00.0
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss0.00.00.00.00.00.00.00.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value249107940155.66861150816091576
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-03-31
Value22418.47
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months9.13.813.8

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-31
Value8.77221
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months3.52.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value21798740145.18952146815701550
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months87.291.598.896.991.586.297.497.698.4

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-312018-09-302018-06-30
Value0.0280.00.0383823
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months0.02.60.00.02.62.41.5

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-30
Value0.5581.0240.470.4740.4790.5660.00.567
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months0.20.11.23.18.50.00.00.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value241040.1080.1410.0341.66454345
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-03-31
Value0.6612.4590.063
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss2.72.43.8

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-31
Value0.3191.183
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss1.31.1

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value231000.1050.1390.0331.597444244
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss96.096.197.298.697.196.298.898.699.0

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-312018-09-302018-06-30
Value0.00.4060.00.00.5170.6090.451
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss0.00.40.00.01.11.41.0

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-30
Value0.0040.0080.0030.0020.0010.0040.00.005
Percentage of DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss0.00.02.81.42.90.00.00.0

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPosition

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPosition


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value27811066943195899195219681881
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPosition100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPosition us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-03-31
Value22418.47
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPosition8.13.70.9

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-31
Value8.77221
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPosition3.11.9

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value24510146842194880191119281855
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPosition88.191.698.397.199.397.997.998.098.6

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-312018-09-302018-06-30
Value0.0280.09.844383823
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPosition0.02.60.01.12.02.01.2

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.5940.5770.710.7980.8450.8410.8780.9330.979
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPosition0.20.11.01.80.40.10.00.00.1

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-30
Value1.0221.0240.470.4740.4790.5660.00.567
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPosition0.40.10.71.10.20.00.00.0

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value271082.5995.4525.86623806766
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-03-31
Value0.6612.4590.063
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss2.42.30.3

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-31
Value0.3191.183
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss1.21.1

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value261042.4795.3435.76423796666
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss95.896.195.498.098.398.699.299.099.2

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-312018-09-302018-06-30
Value0.00.4060.00.1480.5170.6090.451
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss0.00.40.00.60.60.90.7

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value0.1590.1920.1170.1070.1010.120.0840.0590.047
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss0.60.24.52.01.70.50.10.10.1

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-30
Value0.0050.0080.0030.0020.0010.0040.00.005
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss0.00.00.10.00.00.00.00.0

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions us-gaap:FinancialInstrument

us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions

us-gaap:DebtSecurities


None
Period End2020-06-302020-03-312019-09-302019-06-302019-03-312018-12-31
Value75.0325.043.063.0306.0653.0
Percentage of DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions100.0100.0100.0100.0100.0100.0

us-gaap:DebtSecuritiesHeldToMaturityAllowanceForCreditLoss

us-gaap:DebtSecuritiesHeldToMaturityAllowanceForCreditLoss


None
Period End2020-06-302020-03-312019-12-31
Value4940000.06039000.00
Percentage of DebtSecuritiesHeldToMaturityAllowanceForCreditLoss100.0100.00.0

us-gaap:DebtSecuritiesHeldToMaturityAllowanceForCreditLoss nwli:CreditRating

nwli:AARating


None
Period End2020-06-302020-03-31
Value56000.057000.0
Percentage of DebtSecuritiesHeldToMaturityAllowanceForCreditLoss1.10.9

nwli:ARating


None
Period End2020-06-302020-03-31
Value985000.01201000.0
Percentage of DebtSecuritiesHeldToMaturityAllowanceForCreditLoss19.919.9

nwli:BBBRating


None
Period End2020-06-302020-03-31
Value3580000.04468000.0
Percentage of DebtSecuritiesHeldToMaturityAllowanceForCreditLoss72.574.0

nwli:BBRatingAndBelow


None
Period End2020-06-302020-03-31
Value319000.0313000.0
Percentage of DebtSecuritiesHeldToMaturityAllowanceForCreditLoss6.55.2

us-gaap:DebtSecuritiesHeldToMaturityAllowanceForCreditLoss us-gaap:CumulativeEffectPeriodOfAdoption

srt:CumulativeEffectPeriodOfAdoptionAdjustment


None
Period End2020-03-312019-12-31
Value03334000.0
Percentage of DebtSecuritiesHeldToMaturityAllowanceForCreditLoss0.00.0

us-gaap:DebtSecuritiesHeldToMaturityAllowanceForCreditLoss us-gaap:FinancialInstrument

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-31
Value3992000.04788000.0
Percentage of DebtSecuritiesHeldToMaturityAllowanceForCreditLoss80.879.3

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-31
Value879000.01173000.0
Percentage of DebtSecuritiesHeldToMaturityAllowanceForCreditLoss17.819.4

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-31
Value65000.074000.0
Percentage of DebtSecuritiesHeldToMaturityAllowanceForCreditLoss1.31.2

us-gaap:DeferredPolicyAcquisitionCosts

us-gaap:DeferredPolicyAcquisitionCosts


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-312013-12-312012-12-31
Value679782723736752793841842848840819813808821835795794816853835802785705
Percentage of DeferredPolicyAcquisitionCosts100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredSalesInducementsNet

us-gaap:DeferredSalesInducementsNet


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-312013-12-312012-12-31
Value94114104108114123133137138138135134140144147138141150159156159169152
Percentage of DeferredSalesInducementsNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeAssetMeasurementInput us-gaap:Range, us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique

us-gaap:DerivativeAssetMeasurementInput

srt:Maximum, us-gaap:FairValueInputsLevel3, nwli:MeasurementInputImpliedVolatility, nwli:BrokerPrices


None
Period End2020-06-302020-03-312019-12-31
Value0.53690.53690.199
Percentage of DerivativeAssetMeasurementInput100.0100.0100.0

srt:Minimum, us-gaap:FairValueInputsLevel3, nwli:MeasurementInputImpliedVolatility, nwli:BrokerPrices


None
Period End2020-06-302020-03-312019-12-31
Value0.12960.12960.131
Percentage of DerivativeAssetMeasurementInput24.124.165.8

srt:WeightedAverage, us-gaap:FairValueInputsLevel3, nwli:MeasurementInputImpliedVolatility, nwli:BrokerPrices


None
Period End2020-06-302020-03-312019-12-31
Value0.18550.16060.1525
Percentage of DerivativeAssetMeasurementInput34.629.976.6

us-gaap:DerivativeAssets

us-gaap:DerivativeAssets


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value66241571068971141361021161941631491491209063423825114
Percentage of DerivativeAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeAssets nwli:PricingSource

nwli:PricedByThirdPartyVendors


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value66241571068971141361021161941631491491209063423825114
Percentage of DerivativeAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeAssets nwli:PricingSource, us-gaap:FairValueByFairValueHierarchyLevel

nwli:PricedByThirdPartyVendors, us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value66241571068971141361021161941631491491209063423825114
Percentage of DerivativeAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeAssets us-gaap:BalanceSheetLocation, us-gaap:DerivativeInstrumentRisk, us-gaap:HedgingDesignation

nwli:DerivativesIndexOptions, nwli:EquityIndexOptions, us-gaap:Nondesignated


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value66241571068971141361021161941631491491209063423825114
Percentage of DerivativeAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeAssets us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value66241571068971141361021161941631491491209063423825114
Percentage of DerivativeAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeAssets us-gaap:FairValueByFairValueHierarchyLevel, us-gaap:ValuationTechnique

us-gaap:FairValueInputsLevel3, nwli:BrokerPrices


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value662415714
Percentage of DerivativeAssets100.0100.0100.0100.0

us-gaap:DerivativeAssets us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value66241571068971141361021161941631491491209063423825114
Percentage of DerivativeAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value66241571068971141361021161941631491491209063423825114
Percentage of DerivativeAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeAssets us-gaap:HedgingDesignation

us-gaap:Nondesignated


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value66241571068971141361021161941631491491209063423825114
Percentage of DerivativeAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeLiabilities

us-gaap:DerivativeLiabilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value876115511010086441471191342111751571541229676635851133
Percentage of DerivativeLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeLiabilities us-gaap:BalanceSheetLocation, us-gaap:DerivativeInstrumentRisk, us-gaap:HedgingDesignation

nwli:UniversalLifeAndAnnuityContracts, nwli:FixedIndexProducts, us-gaap:Nondesignated


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value876115511010086441471191342111751571541229676635851133
Percentage of DerivativeLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeLiabilities us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value876115511010086441471191342111751571541229676635851133
Percentage of DerivativeLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeLiabilities us-gaap:HedgingDesignation

us-gaap:Nondesignated


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value876115511010086441471191342111751571541229676635851133
Percentage of DerivativeLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized

us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value5.53.1119.58.07.91115141315161512126.44.86.27.76.27.38.49.37.7
Percentage of EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EquitySecuritiesFvNiCost

us-gaap:EquitySecuritiesFvNiCost


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value15151614141414131312
Percentage of EquitySecuritiesFvNiCost100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-31
Value662415710689711413610211619416314914912090634238257295114109146169
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue us-gaap:FairValueByAssetClass

nwli:DerivativesIndexOptions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-31
Value662415710689711413610211619416314914912090634238257295114109146169
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-31
Value936817112311297561621331472261911731671341028169665795119142135171193
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue us-gaap:FairValueByLiabilityClass

nwli:ContingentConsideration


None
Period End2020-06-302020-03-312019-12-312019-06-302019-03-312018-12-31
Value0.04.1744.0763.8713.70.0
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue0.06.12.43.43.80.0

nwli:PolicyholderAccountBalances


None
Period End2020-06-302020-03-312019-12-312019-06-302019-03-312018-12-31
Value87611551008644
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue94.189.591.189.588.179.0

us-gaap:EmployeeStock


None
Period End2020-06-302020-03-312019-12-312019-06-302019-03-312018-12-31
Value5.4973.081117.9917.89811
Percentage of FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue5.94.56.67.18.121.0

us-gaap:FiniteLivedIntangibleAssetsAccumulatedAmortization us-gaap:BusinessAcquisition

us-gaap:FiniteLivedIntangibleAssetsAccumulatedAmortization

nwli:OzarkNationalLifeInsuranceCompany


None
Period End2020-06-302020-03-312019-12-31
Value1033000.0851000.0669000.0
Percentage of FiniteLivedIntangibleAssetsAccumulatedAmortization100.0100.0100.0

us-gaap:FiniteLivedIntangibleAssetsAccumulatedAmortization us-gaap:BusinessAcquisition, us-gaap:FiniteLivedIntangibleAssetsByMajorClass

nwli:OzarkNationalLifeInsuranceCompany, us-gaap:TechnologyBasedIntangibleAssets


None
Period End2020-06-302020-03-312019-12-31
Value769000.0633000.0498000.0
Percentage of FiniteLivedIntangibleAssetsAccumulatedAmortization74.474.474.4

nwli:OzarkNationalLifeInsuranceCompany, us-gaap:TrademarksAndTradeNames


None
Period End2020-06-302020-03-312019-12-31
Value264000.0218000.0171000.0
Percentage of FiniteLivedIntangibleAssetsAccumulatedAmortization25.625.625.6

us-gaap:GoodwillGross us-gaap:BusinessAcquisition

us-gaap:GoodwillGross

nwli:OzarkNationalLifeInsuranceCompany


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value1313130.0
Percentage of GoodwillGross100.0100.0100.00.0

us-gaap:HeldToMaturitySecurities

us-gaap:HeldToMaturitySecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value690369967106722473427428728572817315728072477264723072777159710671777195717371906841
Percentage of HeldToMaturitySecurities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecurities nwli:CreditRating

nwli:AAARating


None
Period End2020-06-302020-03-31
Value9397
Percentage of HeldToMaturitySecurities1.41.4

nwli:AARating


None
Period End2020-06-302020-03-31
Value17391853
Percentage of HeldToMaturitySecurities25.226.5

nwli:ARating


None
Period End2020-06-302020-03-31
Value22342213
Percentage of HeldToMaturitySecurities32.431.6

nwli:BBBRating


None
Period End2020-06-302020-03-31
Value27332758
Percentage of HeldToMaturitySecurities39.639.4

nwli:BBRatingAndBelow


None
Period End2020-06-302020-03-31
Value10273
Percentage of HeldToMaturitySecurities1.51.0

us-gaap:HeldToMaturitySecurities us-gaap:BusinessAcquisition

nwli:OzarkNationalLifeInsuranceCompany


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value329324307290289265
Percentage of HeldToMaturitySecurities4.84.64.34.03.93.6

us-gaap:HeldToMaturitySecurities us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value2.3072.5562.7753.0993.3053.643.889
Percentage of HeldToMaturitySecurities0.00.00.00.00.00.00.1

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value3.0243.0313.0323.0393.0463.051
Percentage of HeldToMaturitySecurities0.00.00.00.00.00.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value45594547460746544688474147154655463345214430
Percentage of HeldToMaturitySecurities66.065.064.864.463.963.864.763.963.362.161.1

us-gaap:ForeignGovernmentDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value1.1331.1391.1441.1491.1541.159
Percentage of HeldToMaturitySecurities0.00.00.00.00.00.0

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value8548918889139149119309649951062
Percentage of HeldToMaturitySecurities12.412.712.512.612.512.312.813.313.614.7

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value9961038106610981131115711761198122212511280
Percentage of HeldToMaturitySecurities14.414.815.015.215.415.616.116.516.717.217.7

us-gaap:USGovernmentAgenciesDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value8189100105121130
Percentage of HeldToMaturitySecurities1.21.31.41.51.61.8

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value401418431441475476457457458462467
Percentage of HeldToMaturitySecurities5.86.06.16.16.56.46.36.36.36.46.5

us-gaap:USTreasurySecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value3.7923.7873.7823.7773.7723.7671.3411.3411.341.3381.337
Percentage of HeldToMaturitySecurities0.10.10.10.10.10.10.00.00.00.00.0

us-gaap:HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain

us-gaap:HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value53625830331424912857486797202246250223220439468366247322357
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value0.0420.0060.0620.0780.0850.0650.088
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain0.00.00.00.00.00.10.2

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value0.0520.00.0520.0570.0580.021
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain0.00.00.00.00.00.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value3781402122111637927263452121
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain70.554.370.067.365.561.748.254.650.753.960.3

us-gaap:ForeignGovernmentDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value0.1540.1230.0550.0560.0440.038
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain0.00.00.00.00.00.0

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value6422363630135.9285.2519.31630
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain12.18.612.111.712.110.610.310.913.915.1

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value657032413420138.228111527
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain12.127.310.813.314.015.924.017.117.816.313.6

us-gaap:USGovernmentAgenciesDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value3.5013.271.6861.8831.8180.678
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain0.71.30.60.60.70.5

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value2321192118149.7648.136111421
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain4.58.46.47.07.611.017.016.917.214.410.8

us-gaap:USTreasurySecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.190.2170.140.1560.1620.1260.1160.1130.1310.150.177
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain0.00.10.00.00.10.10.20.20.20.20.1

us-gaap:HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss

us-gaap:HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value7.125721.6020.8912.801271141421217515121429423.5041035864623
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value0.00.0210.0010.00.00.0030.01
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss0.00.00.10.00.00.00.0

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value0.00.0120.00.00.00.0
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss0.00.00.00.00.00.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value7.068650.7180.4461.99620879284497.876
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss99.289.544.850.171.372.976.164.870.165.852.2

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.07.360.0830.0110.0562.3661216140.894
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss0.010.15.21.22.08.511.311.412.15.9

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.00.0490.7160.3810.7045.026112819156.216
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss0.00.144.742.825.118.110.420.216.421.041.2

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.0570.1740.0840.0530.0450.1362.3765.1471.7051.580.1
Percentage of HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss0.80.25.25.91.60.52.13.61.42.10.7

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value0.0571.0271.0850.7822.742646443629121.9052.6364.2127.3133.0748.49712231620
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-31
Value0.00.00.00.0030.01
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss0.00.00.00.00.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.00.9550.3810.3511.93919312723176.58
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss0.093.035.144.970.872.168.460.963.960.152.1

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.00.00.00.00.0562.3324.5732.6292.1590.487
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss0.00.00.00.02.08.79.85.96.03.9

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.00.00.6530.3780.75.0199.91410105.478
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss0.00.060.248.325.518.721.232.429.734.543.4

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.0570.0720.0510.0530.0450.1330.2520.3280.1840.1870.086
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss100.07.04.76.81.60.50.50.70.50.60.7

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value15913631288020617333906452740623344111987193015971768243345953243217781135
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-31
Value0.01.8181.3491.8621.976
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue0.00.11.10.10.1

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-31
Value0.03.019
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue0.00.2

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value1571075482912312022795297027412253680
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue98.978.937.936.459.669.371.665.667.567.460.8

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.02762.3452.41711199495569535102
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue0.020.31.83.05.411.512.712.613.29.2

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.01.229694770319514864704577322
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue0.00.154.058.534.118.413.219.117.317.328.8

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value1.7495.5976.7251.6891.6661198120796911
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue1.10.45.22.10.80.72.52.72.02.11.0

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value7.068710.5170.1090.0610.974679885462.459101225340.431.7932363303.307
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-31
Value0.00.0210.0010.00.0
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss0.00.00.20.00.0

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-31
Value0.00.012
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss0.00.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value7.068640.3370.0950.0570.93556561321.296
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss100.089.565.287.293.495.581.566.572.769.452.7

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.07.360.0830.0110.00.0348.37113120.407
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss0.010.316.110.10.03.512.414.014.716.6

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.00.0490.0630.0030.0040.0072.032149.1695.8630.738
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss0.00.112.22.86.60.73.014.610.812.630.0

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.00.1020.0330.00.00.0032.1244.8191.5211.3930.014
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss0.00.16.40.00.00.33.14.91.83.00.6

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value157134465121589283337923422269845675877514311580525357619861341183
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-31
Value0.01.8181.3490.00.0
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue0.00.12.00.00.0

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-31
Value0.03.019
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue0.00.2

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value1571058319.2211752144249923251833248
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue100.078.747.676.372.584.475.765.968.067.954.5

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.02762.3452.4170.05.33239653050268
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue0.020.53.620.00.06.014.014.014.715.0

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.01.229250.4494.3075.626202649516389130
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue0.00.139.23.727.56.37.217.115.114.528.5

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.03.8845.0130.00.02.9258811374646.308
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue0.00.37.60.00.03.33.13.02.22.41.4

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value1.74918626819116441073734640646662113155166188191292377445437951
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-03-312018-12-31
Value0.00.00.01.8621.976
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue0.00.00.00.10.2

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.01617201111126650471415420431
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue0.090.727.529.458.668.560.664.264.965.165.1

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value0.00.00.00.01119398393234
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue0.00.00.00.05.911.89.25.45.15.1

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value0.00.0434666313311215187187192
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue0.00.069.768.234.719.129.029.329.229.029.0

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value1.7491.7131.7121.6891.6668.533106.2974.7714.7684.869
Percentage of HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue100.09.32.72.50.90.51.00.90.70.70.7

us-gaap:HeldToMaturitySecuritiesFairValue

us-gaap:HeldToMaturitySecuritiesFairValue


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value74327181740775377589752972287186726173027434749874667472733775427634752573357466733573357175
Percentage of HeldToMaturitySecuritiesFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecuritiesFairValue us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:FairValueInputsLevel2


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value743271817407753675877527722671847259729974317498746674727337754276347525733574667175
Percentage of HeldToMaturitySecuritiesFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value0.00.01.5641.5561.9021.9061.9181.9252.2642.2940.00.00.00.00.00.00.00.00.00.0
Percentage of HeldToMaturitySecuritiesFairValue0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:HeldToMaturitySecuritiesFairValue us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value689869907106722473427428728572817315728072477264723072777159710671777195717371906841
Percentage of HeldToMaturitySecuritiesFairValue92.897.395.995.896.798.7100.8101.3100.799.797.596.996.897.497.694.294.095.697.896.395.3

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value743271817407753775897529722871867261730274347498746674727337754276347525733574667175
Percentage of HeldToMaturitySecuritiesFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:HeldToMaturitySecuritiesFairValue us-gaap:FinancialInstrument

us-gaap:AssetBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value2.3492.5412.8363.1773.393.7023.967
Percentage of HeldToMaturitySecuritiesFairValue0.00.00.00.00.00.00.1

us-gaap:CommercialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value3.0763.0193.0843.0963.1043.072
Percentage of HeldToMaturitySecuritiesFairValue0.00.00.00.00.00.0

us-gaap:CorporateDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value49304622481948654850480046564589458245234544
Percentage of HeldToMaturitySecuritiesFairValue66.364.465.164.663.963.864.463.963.162.061.1

us-gaap:ForeignGovernmentDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value1.2871.2621.1991.2051.1981.197
Percentage of HeldToMaturitySecuritiesFairValue0.00.00.00.00.00.0

us-gaap:PublicUtilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value9199069249509449229239539901092
Percentage of HeldToMaturitySecuritiesFairValue12.412.612.512.612.512.312.813.313.614.7

us-gaap:ResidentialMortgageBackedSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value10611108109811401165117211781177121412521301
Percentage of HeldToMaturitySecuritiesFairValue14.315.414.815.115.415.616.316.416.717.117.5

us-gaap:USGovernmentAgenciesDebtSecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-31
Value8593102107122131
Percentage of HeldToMaturitySecuritiesFairValue1.11.31.41.41.61.7

us-gaap:USStatesAndPoliticalSubdivisions


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value425439450463494490464460467475489
Percentage of HeldToMaturitySecuritiesFairValue5.76.16.16.16.56.56.46.46.46.56.6

us-gaap:USTreasurySecurities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value3.9824.0043.9223.9333.9343.8931.4571.4541.4711.4881.514
Percentage of HeldToMaturitySecuritiesFairValue0.10.10.10.10.10.10.00.00.00.00.0

us-gaap:IncomeTaxReceivable

us-gaap:IncomeTaxReceivable


None
Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value130.0119.9370.0170.013100.07.858140.00.00.00.02.51112190.0
Percentage of IncomeTaxReceivable100.00.0100.0100.00.0100.00.0100.0100.00.0100.0100.00.00.00.00.0100.0100.0100.00.0

us-gaap:Investments

us-gaap:Investments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value10777106241105811126111831120810578107131071910811108171076910717107421062710576105791038010289102539926
Percentage of Investments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LiabilitiesFairValueDisclosure

us-gaap:LiabilitiesFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value9368171123112975616213314722619117316713410281696657142
Percentage of LiabilitiesFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LiabilitiesFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value9368171123112975616213314722619117316713410281696657142
Percentage of LiabilitiesFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LiabilityForFuturePolicyBenefits us-gaap:ConsolidationItems

us-gaap:LiabilityForFuturePolicyBenefits

us-gaap:OperatingSegments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value988699681012710162102481035297449935995399921009899919916991098599798975997029699964196219542952294049125
Percentage of LiabilityForFuturePolicyBenefits100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LiabilityForFuturePolicyBenefits us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, nwli:AcquiredBusinesses


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value7167117067006966940.0
Percentage of LiabilityForFuturePolicyBenefits7.27.17.06.96.86.70.0

us-gaap:OperatingSegments, nwli:Annuities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value7113722073517442756376917810797080478121823281788125814481098065805079998005797679647916792078487676
Percentage of LiabilityForFuturePolicyBenefits71.972.472.673.273.874.380.280.280.881.381.581.981.982.282.382.382.582.482.582.782.883.083.283.584.1

us-gaap:OperatingSegments, nwli:DomesticLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value122911961198114411081075103910451004964950909881852830809782766748720702675648611535
Percentage of LiabilityForFuturePolicyBenefits12.412.011.811.310.810.410.710.510.19.69.49.18.98.68.48.38.07.97.77.57.37.16.86.55.9

us-gaap:OperatingSegments, nwli:InternationalLifeInsurance


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-12-31
Value827840870874879890894918901906915904910913919923926936944944954949953944913
Percentage of LiabilityForFuturePolicyBenefits8.48.48.68.68.68.69.29.29.19.19.19.09.29.29.39.49.59.79.79.89.910.010.010.010.0

us-gaap:LiabilityForFuturePolicyBenefitsLife

us-gaap:LiabilityForFuturePolicyBenefitsLife


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value845842838832827828135135135136135135135136136136136137138137138
Percentage of LiabilityForFuturePolicyBenefitsLife100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LoansInsurancePolicy

us-gaap:LoansInsurancePolicy


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value767880808081545455555657575758596060616163
Percentage of LoansInsurancePolicy100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LoansReceivableFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:LoansReceivableFairValueDisclosure

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value181313141419129.4294.1525.6885.60310141414118.6447.8952.9571.4722.3
Percentage of LoansReceivableFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LoansReceivableFairValueDisclosure us-gaap:FairValueByMeasurementBasis

us-gaap:CarryingReportedAmountFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value181313131319129.0533.9695.5335.4319.786141414128.2717.5022.7791.352.171
Percentage of LoansReceivableFairValueDisclosure98.498.798.998.898.898.596.696.095.697.396.997.097.096.696.3104.095.795.094.091.794.4

us-gaap:EstimateOfFairValueFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value181313141419129.4294.1525.6885.60310141414118.6447.8952.9571.4722.3
Percentage of LoansReceivableFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:MortgageLoansOnRealEstateCommercialAndConsumerNet

us-gaap:MortgageLoansOnRealEstateCommercialAndConsumerNet


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value27327627222421420520320019620420818818316317414613011010888149
Percentage of MortgageLoansOnRealEstateCommercialAndConsumerNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:MortgageLoansOnRealEstateCommercialAndConsumerNet us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable

us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-31
Value273276272
Percentage of MortgageLoansOnRealEstateCommercialAndConsumerNet100.0100.0100.0

us-gaap:NotesReceivableGross nwli:MortgageLoansByLoanToValueRatio, us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable

us-gaap:NotesReceivableGross

nwli:MortgageLoansByLoansToValueRatioEightyToNinetyPercent, us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value0.00.00.05.375
Percentage of NotesReceivableGross0.00.00.0100.0

nwli:MortgageLoansByLoansToValueRatioFiftyToSixtyPercent, us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value50455622
Percentage of NotesReceivableGross0.00.00.0420.7

nwli:MortgageLoansByLoansToValueRatioLessThanFiftyPercent, us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value52575266
Percentage of NotesReceivableGross0.00.00.01234.8

nwli:MortgageLoansByLoansToValueRatioSeventyToEightyPercent, us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value4547466.642
Percentage of NotesReceivableGross0.00.00.0123.6

nwli:MortgageLoansByLoansToValueRatioSixtyToSeventyPercent, us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value126127117102
Percentage of NotesReceivableGross0.00.00.01913.6

us-gaap:NotesReceivableGross us-gaap:FinancingReceivableRecordedInvestmentByClassOfFinancingReceivable

us-gaap:CommercialRealEstate


None
Period End2020-06-302020-03-312019-12-312018-12-31
Value275277273203
Percentage of NotesReceivableGross0.00.00.03792.7

us-gaap:OtherAssets

us-gaap:OtherAssets


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value163165181166171179131142140142137139133134134919390929489
Percentage of OtherAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherCommitment us-gaap:OtherCommitments

us-gaap:OtherCommitment

nwli:CapitalContributionsToInvestmentFunds


None
Period End2020-06-30
Value59
Percentage of OtherCommitment100.0

nwli:ExistingLoans


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value8.80.00.30.40.42.94.36.28.71.21.31.40.41.00.90.61.22.91.74.9
Percentage of OtherCommitment14.90.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

nwli:NewLoans


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value0.00.07.2731416134.311168.0140.09.58.23220252329
Percentage of OtherCommitment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OtherLiabilities

us-gaap:OtherLiabilities


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value130120126127120121111123126139138150119145104103981029610598
Percentage of OtherLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherLiabilitiesFairValueDisclosure

us-gaap:OtherLiabilitiesFairValueDisclosure


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value5.4977.255151311111115141315161512126.4344.8196.1627.6696.2119.256
Percentage of OtherLiabilitiesFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherLiabilitiesFairValueDisclosure us-gaap:FairValueByFairValueHierarchyLevel

us-gaap:FairValueInputsLevel3


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value5.4977.255151311111115141315161512126.4344.8196.1627.6696.2119.256
Percentage of OtherLiabilitiesFairValueDisclosure100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherLongTermInvestments

us-gaap:OtherLongTermInvestments


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302014-12-31
Value706662626268565449515148535353514847262728
Percentage of OtherLongTermInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherLongTermInvestments us-gaap:InvestmentType

us-gaap:RealEstate


None
Period End2020-06-302020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value34343434344035363737