AJG


Line plots across dimensions of each concept
Tables

Table of contents



us-gaap:CommonStockValue

us-gaap:CommonStockSharesIssued
us-gaap:StatementEquityComponents

us-gaap:CommonStockSharesOutstanding

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic

us-gaap:EarningsPerShareBasic

us-gaap:EarningsPerShareDiluted

us-gaap:Revenues

us-gaap:InterestExpense

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:IncomeTaxExpenseBenefit

us-gaap:NetIncomeLoss

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

us-gaap:Liabilities

us-gaap:LiabilitiesAndStockholdersEquity

us-gaap:StockholdersEquity

us-gaap:AssetsCurrent

us-gaap:CashAndCashEquivalentsAtCarryingValue

us-gaap:OtherAssetsCurrent

us-gaap:PropertyPlantAndEquipmentNet

us-gaap:Goodwill
us-gaap:StatementBusinessSegments
us-gaap:StatementGeographical
us-gaap:StatementGeographical, us-gaap:StatementBusinessSegments

us-gaap:IntangibleAssetsNetExcludingGoodwill
us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:OtherAssetsNoncurrent

us-gaap:LiabilitiesCurrent
us-gaap:LineOfCreditFacility, us-gaap:ShortTermDebtType
us-gaap:LongTermDebt
us-gaap:ShortTermDebtType

us-gaap:LongTermDebtNoncurrent

us-gaap:MinorityInterest

us-gaap:OtherLiabilitiesNoncurrent

us-gaap:StockholdersEquity

us-gaap:CommonStockValue

us-gaap:RetainedEarningsAccumulatedDeficit

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax
us-gaap:StatementEquityComponents

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:NetCashProvidedByUsedInOperatingActivities

us-gaap:NetIncomeLoss

us-gaap:ProfitLoss
us-gaap:StatementEquityComponents

us-gaap:IncreaseDecreaseInOtherOperatingCapitalNet

us-gaap:NetCashProvidedByUsedInInvestingActivities

us-gaap:NetCashProvidedByUsedInFinancingActivities

us-gaap:ProceedsFromIssuanceOfLongTermDebt

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
us-gaap:PlanName

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
us-gaap:PlanName

us-gaap:ShareBasedCompensation

us-gaap:OperatingLeaseRightOfUseAsset

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

ajg:AmortizationOfDeferredCompensationAndRestrictedStock

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitments
us-gaap:GuaranteeObligationsByNature
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased
us-gaap:OtherCommitments

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFive
us-gaap:GuaranteeObligationsByNature

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFour
us-gaap:GuaranteeObligationsByNature

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearOne
us-gaap:GuaranteeObligationsByNature
us-gaap:OtherCommitments

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThereafter
us-gaap:GuaranteeObligationsByNature
us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThree
us-gaap:GuaranteeObligationsByNature

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearTwo
us-gaap:GuaranteeObligationsByNature

ajg:AmountOfGainLossRecognizedEffectivenessTesting
us-gaap:IncomeStatementLocation

ajg:BusinessAcquisitionsProFormaNetIncomeLossToControllingInterest

ajg:BusinessCombinationAggregateEarnoutObligationMaximum

ajg:BusinessCombinationAggregateEarnoutObligationRecordedMaximum
us-gaap:AwardType
ajg:CashAndEquityAwardWithAggregateFairValueVestedAndDistributedToParticipants
us-gaap:AwardType
ajg:CashBasedCompensationAwardExpenses
us-gaap:TitleOfIndividual, us-gaap:AwardType

ajg:ChangeInEstimatedAcquisitionEarnoutPayables
us-gaap:AwardType
ajg:CompensationApprovedByCommitteeValue

ajg:ContractWithCustomerImpactOfChangeInForeignExchangeRates
us-gaap:StatementBusinessSegments

ajg:ContractWithCustomerLiabilityAdditions
us-gaap:StatementBusinessSegments

ajg:CostReimbursements

ajg:DeferredCompensationAndRestrictedStockExpensesBenefit
us-gaap:StatementEquityComponents

ajg:EarnoutPaymentsForAcquisitions
us-gaap:Range, us-gaap:BusinessAcquisition, us-gaap:ValuationTechnique
ajg:FairValueInputsAttritionRate

ajg:IncreaseDecreaseInPremiumsAndFeeReceivable

ajg:NetBorrowingsOnPremiumFinancingDebtFacility

ajg:NetChangeInAccruedCompensationAndOtherAccruedLiabilities

ajg:NetProceedsFromSalesOfOperations

ajg:PaymentsToAcquireBusinessesNetOfCashAndRestrictedCashAcquired

ajg:RecordedEarnOutPayable

ajg:RevenueFromContractWithCustomerBeforeReimbursementsExcludingAssessedTax
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:AwardType
ajg:ShareBasedCompensationArrangementByShareBasedPaymentAwardAggregateFairValue
us-gaap:AwardType
ajg:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue

ajg:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue
us-gaap:AwardType
ajg:UnearnedDeferredCompensationShare
us-gaap:AwardType
ajg:UnearnedDeferredCompensationValue

ajg:WeightedAverageNumberOfCommonAndCommonEquivalentSharesOutstanding

us-gaap:AdjustmentForAmortization
us-gaap:AwardType
us-gaap:AllocatedShareBasedCompensationExpense

us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount

us-gaap:BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued

us-gaap:BusinessAcquisitionProFormaEarningsPerShareBasic

us-gaap:BusinessAcquisitionProFormaEarningsPerShareDiluted

us-gaap:BusinessAcquisitionsProFormaNetIncomeLoss

us-gaap:BusinessAcquisitionsProFormaRevenue
us-gaap:BusinessAcquisition

us-gaap:BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable
us-gaap:BusinessAcquisition

us-gaap:BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1

us-gaap:BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect

us-gaap:CommonStockDividendsPerShareDeclared

us-gaap:ComprehensiveIncomeNetOfTax

us-gaap:ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest

us-gaap:ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest

us-gaap:ContractWithCustomerLiabilityIncreaseDecreaseForContractAcquiredInBusinessCombination
us-gaap:StatementBusinessSegments

us-gaap:ContractWithCustomerLiabilityRevenueRecognized
us-gaap:StatementBusinessSegments

us-gaap:CostOfGoodsAndServicesSold

us-gaap:CostOfRevenue

us-gaap:CostsAndExpenses

us-gaap:Depreciation

us-gaap:DepreciationAmortizationAndAccretionNet

us-gaap:DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
us-gaap:DerivativeInstrumentRisk, us-gaap:IncomeStatementLocation
us-gaap:IncomeStatementLocation

us-gaap:DividendsCommonStockCash
us-gaap:StatementEquityComponents

us-gaap:EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents

us-gaap:ForeignCurrencyTransactionGainLossUnrealized
us-gaap:LineOfCreditFacility, us-gaap:SubsequentEventType
us-gaap:GainLossOnDerivativeInstrumentsNetPretax

us-gaap:GainLossOnInvestments

us-gaap:GoodwillAcquiredDuringPeriod
us-gaap:StatementBusinessSegments

us-gaap:GoodwillPurchaseAccountingAdjustments
us-gaap:StatementBusinessSegments

us-gaap:GoodwillTranslationAndPurchaseAccountingAdjustments
us-gaap:StatementBusinessSegments
us-gaap:StatementBusinessSegments
us-gaap:ImpairmentOfIntangibleAssetsFinitelived

us-gaap:IncomeTaxesPaidNet

us-gaap:IncreaseDecreaseInAccruedIncomeTaxesPayable

us-gaap:IncreaseDecreaseInContractWithCustomerLiability

us-gaap:IncreaseDecreaseInDeferredIncomeTaxes

us-gaap:IncreaseDecreaseInOtherOperatingAssets

us-gaap:IncreaseDecreaseInReinsurancePayables

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements

us-gaap:InterestPaid

us-gaap:LaborAndRelatedExpense

us-gaap:MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders
us-gaap:StatementEquityComponents

us-gaap:MinorityInterestDecreaseFromRedemptions
us-gaap:StatementEquityComponents

us-gaap:NetIncomeLossAttributableToNoncontrollingInterest
us-gaap:LineOfCreditFacility, us-gaap:LongtermDebtType, us-gaap:SubsequentEventType, us-gaap:SubsidiarySaleOfStock
us-gaap:NotesIssued1

us-gaap:NumberOfBusinessesAcquired

us-gaap:NumberOfReportableSegments

us-gaap:OperatingExpenses

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax

us-gaap:OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTaxParent
us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax
us-gaap:DerivativeInstrumentRisk, us-gaap:IncomeStatementLocation

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax
us-gaap:StatementEquityComponents
us-gaap:TradingActivityByType
us-gaap:StatementEquityComponents
us-gaap:OtherComprehensiveIncomeLossNetOfTax

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax

us-gaap:OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax

us-gaap:PaymentsForCapitalImprovements

us-gaap:PaymentsForProceedsFromInvestments

us-gaap:PaymentsOfDebtIssuanceCosts

us-gaap:PaymentsOfDividendsCommonStock

us-gaap:PaymentsToAcquireBusinessesGross

us-gaap:PaymentsToMinorityShareholders

us-gaap:ProceedsFromIssuanceOfCommonStock

us-gaap:ProceedsFromLinesOfCredit

us-gaap:RepaymentsOfLinesOfCredit
us-gaap:AwardType
us-gaap:RestrictedStockExpense

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax
us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments
us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments
us-gaap:ConsolidationItems, us-gaap:StatementGeographical, us-gaap:StatementBusinessSegments
us-gaap:ProductOrService
us-gaap:StatementGeographical
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
us-gaap:ValuationTechnique
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

us-gaap:StockGrantedDuringPeriodValueSharebasedCompensation
us-gaap:StatementEquityComponents
us-gaap:StatementEquityComponents
us-gaap:StockIssuedDuringPeriodSharesAcquisitions

us-gaap:StockIssuedDuringPeriodSharesStockOptionsExercised
us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodValueAcquisitions
us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodValueEmployeeStockPurchasePlan
us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodValueStockOptionsExercised
us-gaap:StatementEquityComponents

ajg:AccruedCompensationAndOtherAccruedLiabilities

ajg:AccruedSupplementalDirectBillAndOtherReceivablesCurrent

ajg:BusinessAcquisitionCostOfAcquiredEntityPurchasePriceNet
us-gaap:FiniteLivedIntangibleAssetsByMajorClass, us-gaap:StatementBusinessSegments
ajg:BusinessAcquisitionPurchasePriceAllocationGoodwillNotExpectedTaxDeductibleAmount

ajg:BusinessAcquisitionsPurchasePriceAllocationGoodwillAmount

ajg:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAccruedLiability
us-gaap:BusinessAcquisition

ajg:EquityMethodInvestmentSummarizedFinancialInformationFundingCommitments
us-gaap:ScheduleOfEquityMethodInvestmentEquityMethodInvesteeName, us-gaap:InvestmentType, us-gaap:StatementEquityComponents

ajg:ExpirationLists

ajg:MaximumPotentialEarnoutPayable
us-gaap:LineOfCreditFacility, us-gaap:ShortTermDebtType
ajg:NumberOfLetterOfCreditIssued
us-gaap:ShortTermDebtType

ajg:PremiumFinancingBorrowings

ajg:PremiumsPayableToUnderwritingEnterprises
us-gaap:AwardType
ajg:ProvisionalCompensationCashAwardApprovedForFutureGrantByCompensationCommitteeUnits
us-gaap:TitleOfIndividual, us-gaap:AwardType
us-gaap:TitleOfIndividual, us-gaap:AwardType
ajg:ProvisionalCompensationCashAwardApprovedForFutureGrantByCompensationCommitteeValue

ajg:RefinedCoalProductionRelatedReceivablesCurrent

ajg:SemiAnnualPaymentsOfInterest

ajg:SemiAnnualPaymentsOfInterestNet
us-gaap:AwardType
ajg:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionNonvestedIntrinsicValue

us-gaap:AccountsReceivableBilledForLongTermContractsOrPrograms

us-gaap:AdditionalPaidInCapitalCommonStock
us-gaap:BusinessAcquisition, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique
us-gaap:AlternativeInvestmentMeasurementInput
us-gaap:Range, us-gaap:BusinessAcquisition, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents
us-gaap:BusinessAcquisition

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther
us-gaap:BusinessAcquisition

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities
us-gaap:BusinessAcquisition

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
us-gaap:BusinessAcquisition

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets
us-gaap:BusinessAcquisition

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities
us-gaap:BusinessAcquisition

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
us-gaap:BusinessAcquisition

us-gaap:CapitalizedContractCostAccumulatedAmortization

us-gaap:CapitalizedContractCostNet

us-gaap:ContractWithCustomerLiability
us-gaap:StatementBusinessSegments
us-gaap:LineOfCreditFacility, us-gaap:LongtermDebtType, us-gaap:SubsequentEventType, us-gaap:SubsidiarySaleOfStock
us-gaap:DebtWeightedAverageInterestRate

us-gaap:DeferredRevenue

us-gaap:DeferredRevenueCurrent

us-gaap:DeferredRevenueNoncurrent

us-gaap:DeferredTaxAssetsNetNoncurrent

us-gaap:DerivativeAssetNotionalAmount
us-gaap:BalanceSheetLocation, us-gaap:DerivativeInstrumentRisk
us-gaap:DerivativeInstrumentRisk, us-gaap:FinancialInstrument
us-gaap:DerivativeInstrumentsAndHedges
us-gaap:DerivativeInstrumentRisk, us-gaap:FinancialInstrument, us-gaap:OptionIndexedToIssuersEquityType
us-gaap:DerivativeInstrumentRisk, us-gaap:OptionIndexedToIssuersEquityType

us-gaap:DerivativeLiabilityNotionalAmount
us-gaap:BalanceSheetLocation, us-gaap:DerivativeInstrumentRisk

us-gaap:DerivativeNotionalAmount
us-gaap:DerivativeInstrumentRisk

us-gaap:EquityMethodInvestmentSummarizedFinancialInformationAssets
us-gaap:ScheduleOfEquityMethodInvestmentEquityMethodInvesteeName
us-gaap:ScheduleOfEquityMethodInvestmentEquityMethodInvesteeName, us-gaap:InvestmentType, us-gaap:StatementEquityComponents

us-gaap:EscrowDeposit
us-gaap:FiniteLivedIntangibleAssetsByMajorClass
us-gaap:FiniteLivedIntangibleAssetsAccumulatedAmortization
us-gaap:FiniteLivedIntangibleAssetsByMajorClass
us-gaap:FiniteLivedIntangibleAssetsGross

us-gaap:FiniteLivedNoncompeteAgreementsGross

us-gaap:FiniteLivedTradeNamesGross
us-gaap:BusinessAcquisition
us-gaap:StatementBusinessSegments

us-gaap:OperatingLeaseLiabilityNoncurrent

us-gaap:PremiumsAndOtherReceivablesNet

us-gaap:PrepaidExpenseCurrent
us-gaap:Range, us-gaap:LineOfCreditFacility
us-gaap:ProductLiabilityContingencyAccrualPresentValue
us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligation
us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueAfterFifthYear
us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueInFifthYear
us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueInFourthYear
us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear
us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueInSecondYear
us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased
us-gaap:RecordedUnconditionalPurchaseObligationDueInThirdYear

us-gaap:RestrictedCashCurrent

us-gaap:RevenueRemainingPerformanceObligation
us-gaap:StatementBusinessSegments
us-gaap:AwardType
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
us-gaap:PlanName
us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
us-gaap:TitleOfIndividual, us-gaap:PlanName

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions
us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions
us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

us-gaap:SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1
us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

us-gaap:ShortTermBorrowings

us-gaap:StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest
us-gaap:StatementEquityComponents

us-gaap:UnamortizedDebtIssuanceExpense

us-gaap:UnbilledContractsReceivable

Tables

  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:CommonStockValue ███████▇▇▇▇▇▇▇▇▇▇▇▇▇▇▆▆▆▆▄▃▃▃▃▃▃▂▂▂▂▂▁▁▁▁189188186186185184183182182181180180180179178177177177176176174166164161159135133131127126125124121118114112112110108106105NANANA
us-gaap:CommonStockSharesIssued ███████▇▇▇▇▇▇▇▇▇▇▇▇▇▇▆▆▆▆▄▃▃▃▃▃▃▂▂▂▂▂▁▁▁▁189188186186185184183182182181180180180179178177177177176176174166164161159135133131127126125124121118114112112110108106105NANANA
 us-gaap:CommonStockSharesIssued us-gaap:StatementEquityComponents us-gaap:CommonStock█▁189188NANA185184NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:CommonStockSharesOutstanding ███████▇▇▇▇▇▇▇▇▇▇▇▇▇▇▆▆▆▆▄▃▃▃▃▃▃▂▂▂▂▂▁▁▁▁189188186186185184183182182181180180180179178177177177176176174166164161159135133131127126125124121118114112112110108106105NANANA
us-gaap:WeightedAverageNumberOfSharesOutstandingBasic 188NA186185184NA183182181NA180180179178NA177177177NA176170165NA160154134NA129127126NA123119116NA112111109NA105104NANANA
us-gaap:EarningsPerShareBasic █▃▃▃█▃▃▃▇▃▃▃▄▂▃▃▄▂▂▄▄▁▂▃▃▂▂▃▃▂▂▃▃▁▂▂▂▁▃▂▂▂▂▂1.830.53000000000000020.680.591.810.64000000000000010.70.631.510.57999999999999980.610.610.960.310.530.690.850.260.339999999999999860.760.820.130.300000000000000040.580.710.370.45000000000000020.570.730.320.270.50.60.240.360.410.380.140.510.440.420.280.410.44
us-gaap:EarningsPerShareDiluted █▃▃▃█▃▃▃▇▃▃▃▄▂▃▃▄▂▂▄▄▁▂▃▃▂▂▃▄▂▂▃▃▁▂▂▂▁▃▂▂▂▂▂1.790.51000000000000020.660.581.770.62000000000000010.680.621.480.57000000000000010.610.610.950.310.52999999999999980.690.840.260.35000000000000010.750.810.130.300000000000000040.580.70.360.449999999999999960.570.730.320.270.50.590.240.350.410.370.140.510.440.420.280.410.44
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:Revenues ▇▇▇▆█▆▇▇▇▆▆▆▆▅▅▆▅▅▅▆▅▅▅▅▄▃▃▃▃▂▂▂▂▁▂▂▁▁▁▁▁▁▁▁1866172118251657199016571778166018371599158415841563141213851482142713001334145413711231124512861179915890835779674673650649546578562546447459463459482439453
us-gaap:InterestExpense ██▇▇▆▆▆▅▅▅▅▅▅▄▄▄▄▄▄▄▄▄▄▄▃▂▂▂▁▁▁▁▁▁50484644403636333131313131292828272525252625252521161313111110101010NA10109NA88867
us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest █▂▃▃▇▁▂▃▆▂▂▂▄▂▂▂▃▂▁▃▃▁▁▂3568411410532143901032428276761475268941375528105128302995NANANANANANANANANANANANANANANANANANANANA
 us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,ajg:BrokerageSegment█▃▄▃█▂▃▃▆▃▃▃▄▂▂▃▃▂▁▂▃▁4101511991824121111631703181541411412121171231491781007312215661NANANANANANANANANANANANANANANANANANANANANANA
us-gaap:IncomeTaxExpenseBenefit ▇▅▅▆▅▁▃▅▄▅▄▄▄▆▅▄▅▇▄▄▅▇▅▆▇▇▆▇▇▇▇██▇0-21-22-15-29-84-48-20-43-31-41-41-33-15-32-35-18-2-39-35-19-1-25-5-1-3-1010311114194NA24248NA2422132130
us-gaap:NetIncomeLoss █▃▃▃█▃▃▃▆▃▃▃▄▂▃▃▄▂▂▃▄▁▂▃▃▂▂▂▃▂▁▂▂▁▂▂▂▁▂▂▂▁▂▂346981261103341171271142731051301301715595122150466213313921519310949607493403361712840464115544644294143
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
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 us-gaap:Assets us-gaap:ConsolidationItems,us-gaap:StatementBusinessSegments us-gaap:OperatingSegments,ajg:BrokerageSegment█▇▇▇▇▆▆▆▆▄▄▄▄▃▃▃▃▃▃▃▃▂▃▃▂▁▁1811516741162611646415981137851370013779137841033610275102751005294229183897292258681896986388894809284138377801757715522NANANA4196NANANANANANANANANANANANANA
us-gaap:Liabilities █▇▇▇▇▆▆▆▆▄▄▄▄▄▄▄▄▃▄▃▃▃▃▃▃▂▂▂▂▂▂▁▂▁▁▁▁▁▁▁▁15766144191426114252136731176411502117171154387328638863886598053783374597728706072256802700465116780673267695131477540383860356036933373366032463239302733792544248924492590NANANA
us-gaap:LiabilitiesAndStockholdersEquity ██▇▇▇▆▆▆▆▅▅▅▅▄▄▄▄▄▄▄▄▄▄▄▄▃▂▂▂▂▂▂▂▁▁▁▁▁▁▁▁2083619634191731920018631163341611416230161271289712810128101256911780114891120011384107121091310510107169730100109988100197275686059705562522553525009513346024483424745813691359634603555NANANA
us-gaap:StockholdersEquity ██▇██▇▇▇▇▆▆▆▆▆▅▆▅▅▅▅▅▅▅▅▅▃▃▃▂▂▂▂▂▂▁▁▁▁▁▁▁5029515548434879488044984544444345144105411041103844366235963686359935973638365236383145322932563249214420851932170216641658163614721356124312191202114711061011965NANANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:AssetsCurrent █▇▇▇▇▆▆▆▆▄▄▄▄▃▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▁▂▂▂▁▁▁▂▁▁▁▁105279117932895479669811880848365853351705087508751074483441642134485393943354020426135943811397244403198287525462602230124292324263122252199208824161749172616891823NANANA
us-gaap:CashAndCashEquivalentsAtCarryingValue ▂▅▄▄▇▅▅▅▅▅▄▄▄▄▄▄▃▃▃▂▂▁▂▂█▆▂▂▁▁▂▂▂▂▂▁▁▂▁▂▁▁▁▁352604578512871607605652697681564564587564545531411425480369321276314290973739298286240224302305282301291241263333249296230227237226
us-gaap:OtherAssetsCurrent ▆██▇▇█▇▇▆▅▅▅▅▅▅▅▅▄▅▅▆▄▅▅▃▂▂▂▂▂▁▂▁▁▂▁▁▁▁▁▁799107410369938751024951878749708679679664594633601605503709700731587666670360289261260203227179182157165188146127117126123111NANANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:PropertyPlantAndEquipmentNet █████▇▇▇▇▇▇▇▇▆▆▃▃▄▃▃▃▃▃▃▃▃▃▂▂▂▂▁▁▁▁▁▁▁▁▁▁4544674584584504364294274244124134133873753772132132182022001981901951961931651601481231081051011009591908779757579NANANA
us-gaap:Goodwill ███▇▇▇▆▆▆▆▆▆▆▆▅▅▅▅▅▅▅▅▅▅▄▃▃▂▂▂▂▂▂▂▂▁▁▁▁▁▁5555561853145241480046254501440342364197416041603989389637673762371636933662357935693418344932963027214221451771150614681472137312851195115510921072925883824780NANANA
 us-gaap:Goodwill us-gaap:StatementBusinessSegments ajg:BrokerageSegment███▇▇▆▆▆▆▆▆▆▆▅▅▅▅▅▅▅▅▅▅▄▄▃▃▂▂▂▂▁▁▁▁▁▁5488554852465190474845734452435841894152411441143946386537363734368736643635355235413392342732733005211921221750148414471451135312651174113610741055NA866NANANANANA
 us-gaap:Goodwill us-gaap:StatementGeographical country:GB██▇▇▃▃▃▃▃▃▃▃▂▂▂▂▂▃▃▄▄▃▄▄▄▁▁1199119011501153793762733739783745745745699672666688705749782806828788820833882571597NANANA226NANANANANANANANANANANANANA
 us-gaap:Goodwill us-gaap:StatementGeographical country:US██▇▇▆▆▆▅▄▄▄▄▄▄▄▃▃▃▃▃▂▂▂▁▁▁▁325231962983289128242744265625702341234023112311227422252138208820551999197019081807171016721592155115051469NANANA1177NANANANANANANANANANANANANA
 us-gaap:Goodwill us-gaap:StatementGeographical,us-gaap:StatementBusinessSegments country:GB,ajg:BrokerageSegment██▇▇▂▁▁▁1186117711381144784753726732NA738NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
 us-gaap:Goodwill us-gaap:StatementGeographical,us-gaap:StatementBusinessSegments country:US,ajg:BrokerageSegment█▇▅▄▄▃▂▁32193163295028612794271526262545NA2280NANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
us-gaap:IntangibleAssetsNetExcludingGoodwill ██▇▇▆▆▆▆▅▅▆▆▆▆▅▅▆▆▆▆▆▆▆▆▅▃▃▃▂▂▂▂▂▂▁▁▁▁▁▁▁224623182073200818411773177217311639164416711671166216821627162916591672169817411761172317761771163110931078918784768809722644598561556562489483435431NANANA
 us-gaap:IntangibleAssetsNetExcludingGoodwill us-gaap:FiniteLivedIntangibleAssetsByMajorClass ajg:ExpirationLists▇█▇▆▅▅▅▅▄▄▅▅▅▅▄▄▄▅▅▅▅▅▅▅▄▁▁215522411989192517701702172716851629163316591659165016701614161516411651167817201736169317421733160110721052NANANA784NANANANANANANANANANANANANA
us-gaap:OtherAssetsNoncurrent ▇█▇▇▆▆▆▆▆▆▅▅▅▅▅▆▆▅▅▅▅▄▃▄▄▃▃▂▂▃▂▂▂▂▂▁▁▁▁▁▁674773660670630573584586585567559559561536504630606528492480487408385399397383320302270319283245232251235204208204181190186NANANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:LiabilitiesCurrent █▇▇▇▇▆▆▆▆▄▄▄▄▄▄▃▃▃▃▃▃▃▃▃▃▂▃▂▂▂▂▂▂▁▁▁▂▁▁▁▁98378921891089328637769374227568774249124705470548584784461143984383402241913729390534383642376938753033328425772343221523622090244220442073194322871485157715321689NANANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
 us-gaap:LongTermDebt us-gaap:LineOfCreditFacility,us-gaap:ShortTermDebtType ajg:RentCaptiveFacility,us-gaap:LetterOfCredit█▁▁▁7666NA6666666666666666666666NANANANANANANANANANANANANANANANANA
 us-gaap:LongTermDebt us-gaap:LineOfCreditFacility,us-gaap:ShortTermDebtType ajg:SelfInsuranceDeductibles,us-gaap:LetterOfCredit▁▁██991010NA1099NA912121312121212111111111099999NANANANANANANANANANANANANANANANANA
 us-gaap:LongTermDebt us-gaap:ShortTermDebtType us-gaap:LetterOfCredit▁▁▁███000111NANANA04455555555555555NANANANANANANANANANANANANANANANANANA
us-gaap:LongTermDebtNoncurrent █▇▇▇▇▆▆▆▅▅▅▅▅▄▄▄▄▄▄▄▄▄▄▄▄▃▂▂▂▁▁▁▁▁▁▁▁▁▁▁▁43153816381538153690309131413141279226912741274126442144214420442344207120752125212521252125212521251425825825925725725725675675675675675675550550550NANANA
us-gaap:MinorityInterest ▁▅▆▆█▇▆▆▆▅▅▅▆▆▅▄▄▄▃▄▇▇█4060686877706869695962626564595455554955737475NANANANANANANANANANANANANANANANANANANANANA
us-gaap:OtherLiabilitiesNoncurrent ██▇▇▅▅▅▅▅▇▇▇▇▇▇▆▆▆▆▆▆▆▆▅▄▃▃▃▃▃▃▃▂▂▂▁▂▁▁▁▁1225127111271101937900862931933112811911191115611231077101510009669589489749471012837769672665635591620605557543526491409417383362367350NANANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:StockholdersEquity ██▇██▇▇▇▇▆▆▆▆▆▅▆▅▅▅▅▅▅▅▅▅▃▃▃▂▂▂▂▂▂▁▁▁▁▁▁▁5029515548434879488044984544444345144105411041103844366235963686359935973638365236383145322932563249214420851932170216641658163614721356124312191202114711061011965NANANA
us-gaap:CommonStockValue ███████▇▇▇▇▇▇▇▇▇▇▇▇▇▇▆▆▆▆▄▃▃▃▃▃▃▂▂▂▂▂▁▁▁▁189188186186185184183182182181180180180179178177177177176176174166164161159135133131127126125124121118114112112110108106105NANANA
us-gaap:RetainedEarningsAccumulatedDeficit █▇▇▇▇▆▅▅▅▄▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▁▁▁▁▁▁▁▁▁▁▁▁▁2161190118841839181015581517146614261095106210621002901916889835753774778710636676683648596596583554506510519500470482480471466488468456NANANA
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 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:AccumulatedDefinedBenefitPlansAdjustment▂▂▂▂▁▁▃▃▄▄▄▄▄▄▄▅▅▅▅▅▄▄▄████-55-56-57-58-59-61-48-49-43-43-43-43-44-46-47-38-39-42-42-42-43-43-44-24-24-25-25NANANA-52NANANA-49NANANA-18NANANANANA
 us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents us-gaap:AccumulatedGainLossNetCashFlowHedgeParent▁▆▄▅▇▇██-119-28-63-38-17-5107NA8NANANANA-7NANANANANANANANANANANANANANANANANANANANANANANANANANANANANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:NetCashProvidedByUsedInOperatingActivities ▄▆▆█▂▅▅█▁▅▆▆108350349515-96260191530-217261332332NANANANANANANANANANANA2613076712042251163116NA-47NANANA-7NANANA3NANA
us-gaap:NetCashProvidedByUsedInInvestingActivities █▄▆▁▇▆▆▄████-105-396-247-591-141-256-208-358-86-108-118-118NANANANANANANANANANANA-449-1416-44-421-265-132-32-227-72NA-11NANANA-27NANANA2NANA
us-gaap:NetCashProvidedByUsedInFinancingActivities ▄▃▃▄█▃▂▄▃▃▁▁147981125075-4413269-1-165-165NANANANANANANANANANANA-2551501409361104129-9261-25NA69NANANA118NANANA15NANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:NetCashProvidedByUsedInOperatingActivities ▄▆▆█▂▅▅█▁▅▆▆108350349515-96260191530-217261332332NANANANANANANANANANANA2613076712042251163116NA-47NANANA-7NANANA3NANA
us-gaap:NetIncomeLoss █▃▃▃█▃▃▃▆▃▃▃▄▂▃▃▄▂▂▃▄▁▂▃▃▂▂▂▃▂▁▂▂▁▂▂▂▁▂▂▂▁▂▂346981261103341171271142731051301301715595122150466213313921519310949607493403361712840464115544644294143
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 us-gaap:ProfitLoss us-gaap:StatementEquityComponents us-gaap:RetainedEarnings346NA1261103341171271142731051301301715595122150466213313921NANANANANANANANANANANANANANANANANANANANANANA
us-gaap:IncreaseDecreaseInOtherOperatingCapitalNet ▄▃▂▅▄▄▁▆▄▄▃▃▃▅▃▃▆▄▄▆▅▅▇▂█▆▃▄▄▅▄▄11-3-3227159-5253120-6-6-928-19-145017-140282159-288649-22302131NA29NANANA11NANANA10NANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:NetCashProvidedByUsedInInvestingActivities █▄▆▁▇▆▆▄████-105-396-247-591-141-256-208-358-86-108-118-118NANANANANANANANANANANA-449-1416-44-421-265-132-32-227-72NA-11NANANA-27NANANA2NANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
us-gaap:NetCashProvidedByUsedInFinancingActivities ▄▃▃▄█▃▂▄▃▃▁▁147981125075-4413269-1-165-165NANANANANANANANANANANA-2551501409361104129-9261-25NA69NANANA118NANANA15NANA
us-gaap:ProceedsFromIssuanceOfLongTermDebt █▂▂▃█▁▂57500125600-500NANA3009898NANA1000NANANANANANA0-10070060000NANA0NANANANANANANANANANANANANA
  2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30

Common Stock Value

us-gaap:CommonStockValue



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value189188186186185184183182182181180180179178177177177176176174166164161159135133131127126125124121118114112112110108106105102
Percentage of CommonStockValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.91.01.01.01.01.11.11.11.11.41.41.41.51.61.61.61.71.61.71.61.71.61.61.61.91.92.22.32.42.32.52.42.62.62.72.43.03.03.13.03.2

Shares Issued

Common Stock Shares Issued

us-gaap:CommonStockSharesIssued



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value189188186186185184183182182181180180179178177177177176176174166164161159135133131127126125124121118114112112110108106105102
Percentage of CommonStockSharesIssued100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:CommonStock



Period End2020-03-312019-12-312019-03-312018-12-31
Value189188185184
Percentage of CommonStockSharesIssued100.0100.0100.0100.0

Common Stock Shares Outstanding

us-gaap:CommonStockSharesOutstanding



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value189188186186185184183182182181180180179178177177177176176174166164161159135133131127126125124121118114112112110108106105102
Percentage of CommonStockSharesOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Common Stock Shares Authorized

Weighted Average Number Of Shares Outstanding Basic

us-gaap:WeightedAverageNumberOfSharesOutstandingBasic



Period End2020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-09-302017-06-302017-03-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value188186185184183182181180180179178177177177176170165160154134129127126123119116112111109105104
Percentage of WeightedAverageNumberOfSharesOutstandingBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Earnings Per Share Basic

us-gaap:EarningsPerShareBasic



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value1.830.53000000000000020.680.591.810.64000000000000010.70.631.510.57999999999999980.610.720.960.310.530.690.850.260.339999999999999860.760.820.130.300000000000000040.580.710.370.45000000000000020.570.730.320.270.50.60.240.360.410.380.140.510.440.420.280.410.44
Percentage of EarningsPerShareBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Earnings Per Share Diluted

us-gaap:EarningsPerShareDiluted



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value1.790.51000000000000020.660.581.770.62000000000000010.680.621.480.57000000000000010.610.710.950.310.52999999999999980.690.840.260.35000000000000010.750.810.130.300000000000000040.580.70.360.449999999999999960.570.730.320.270.50.590.240.350.410.370.140.510.440.420.280.410.44
Percentage of EarningsPerShareDiluted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Income Loss From Continuing Operations Per Basic Share

Income Loss From Continuing Operations Per Diluted Share

Revenues

us-gaap:Revenues



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value1866172118251657199016571778166018371599158415841563141213851482142713001334145413711231124512861179915890835779674673650649546578562546447459463459482439453
Percentage of Revenues100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.099.4100.0105.085.8100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Premiums Earned Net

Interest Expense

us-gaap:InterestExpense



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value504846444036363331313131312928282725252526252525211613131111101010101010988867
Percentage of InterestExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.72.82.62.72.02.22.12.01.72.02.02.02.11.82.01.91.92.01.91.81.92.12.12.01.81.81.61.61.51.71.61.61.71.91.81.92.11.91.91.81.51.5

Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments

Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value3568411410532143901032428276961475268941375528105128302995
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax19.14.96.36.416.22.65.16.213.25.14.86.19.93.25.06.49.64.32.17.39.42.52.47.4

us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value4101511991824121111631703181541411612121171231491781007312215661
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest115.4180.8174.1172.8128.2258.1180.7164.7131.6188.4183.6144.6225.0180.1157.1129.6179.5258.1115.9121.9197.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax22.08.811.011.020.76.79.210.317.49.78.910.214.37.18.910.112.57.75.58.411.45.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:OperatingSegments ajg:BrokerageSegment28.60.016.716.129.80.015.617.126.70.015.016.923.713.40.017.019.012.10.014.717.78.1

us-gaap:OperatingSegments, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value25232121222722242123262722222421222419222623
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest7.228.218.919.96.864.424.723.28.928.434.515.643.835.822.716.343.169.021.220.876.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.41.41.21.31.11.71.31.41.21.51.71.81.51.41.81.51.61.81.51.51.91.9
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:OperatingSegments ajg:RiskManagementSegment10.30.08.88.79.30.09.410.19.40.011.813.910.612.50.012.212.713.40.012.514.113.3

us-gaap:OperatingSegments, us-gaap:Corporate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value-80-91-106-97-112-96-95-91-98-95-90-92-88-88-79-75-63-68-64-39-54-53
Percentage of IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest-22.6-109.0-93.0-92.7-35.0-222.5-105.4-87.8-40.5-116.8-118.1-60.1-168.8-115.8-79.8-45.9-122.6-227.1-37.1-42.6-173.8
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax-4.3-5.3-5.9-5.9-5.7-5.8-5.4-5.5-5.3-6.0-5.7-5.9-5.9-5.4-5.8-5.1-4.4-5.3-4.8-2.7-4.0-4.4
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax us-gaap:OperatingSegments us-gaap:Corporate-44.20.0-27.9-34.4-30.20.0-19.3-21.5-23.80.0-21.1-21.5-23.5-25.10.0-17.7-20.3-23.10.0-8.9-18.5-17.7

Income Tax Expense Benefit

us-gaap:IncomeTaxExpenseBenefit



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value0-21-22-15-29-84-48-20-43-31-41-41-33-15-32-35-18-2-39-35-19-1-25-5-1-3-1010311114194242482422132130
Percentage of IncomeTaxExpenseBenefit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.0-1.3-1.2-1.0-1.5-5.1-2.7-1.2-2.4-1.9-2.6-2.6-2.2-0.9-2.3-2.4-1.3-0.2-3.0-2.4-1.4-0.1-2.0-0.5-0.2-0.3-1.21.30.50.31.82.23.00.84.34.41.95.24.82.84.96.7

Net Income Loss

us-gaap:NetIncomeLoss



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value346981261103341171271142731051301301715595122150466213313921519310949607493403361712840464115544644294143
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax18.55.76.96.616.87.17.26.914.96.68.28.211.53.46.98.310.53.64.79.210.21.84.17.39.25.46.78.912.06.05.09.511.05.17.08.37.63.411.910.09.66.19.59.7

Assets

us-gaap:Assets



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value208361963419173192001863116334161141623016127128971281012569117801148911200113841071210913105101071697301001099881001972756860597055625225535250095133460244834247458136913596346035553250
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value181151674116261164641598113785137001377913784103361027510052942291838972922586818969863888948092841383778017577155224196
Percentage of Assets86.985.384.885.885.884.485.084.985.580.180.280.080.079.980.181.081.082.282.283.083.284.083.980.079.380.578.4
Percentage of Assets86.985.384.885.885.884.485.084.985.580.180.280.080.079.980.181.081.082.282.283.083.284.083.980.079.380.578.4
Percentage of Assets us-gaap:OperatingSegments ajg:BrokerageSegment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value909898920847806748748739735735733707691666679663690660640623571547621611598544498
Percentage of Assets4.44.64.84.44.34.64.64.64.65.75.75.65.95.86.15.86.46.06.15.85.95.56.26.18.27.99.3
Percentage of Assets4.44.64.84.44.34.64.64.64.65.75.75.65.95.86.15.86.46.06.15.85.95.56.26.18.27.99.3
Percentage of Assets us-gaap:OperatingSegments ajg:RiskManagementSegment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingSegments, us-gaap:Corporate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value18111994199118881843180016651712160718251801180916661639154814941340128412311198106710489891390905793656
Percentage of Assets8.710.210.49.89.911.010.310.510.014.214.114.414.114.313.813.112.511.811.711.211.010.59.913.912.411.612.3
Percentage of Assets8.710.210.49.89.911.010.310.510.014.214.114.414.114.313.813.112.511.811.711.211.010.59.913.912.411.612.3
Percentage of Assets us-gaap:OperatingSegments us-gaap:Corporate100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Liabilities

us-gaap:Liabilities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value15766144191426114252136731176411502117171154387328638865980537833745977287060722568027004651167806732676951314775403838603560369333733660324632393027337925442489244925902357
Percentage of Liabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets75.773.474.474.273.472.071.472.271.667.767.468.968.468.266.667.965.966.264.765.466.967.767.467.670.569.667.669.468.169.067.371.370.572.371.373.768.969.270.872.872.5

Liabilities And Stockholders Equity

us-gaap:LiabilitiesAndStockholdersEquity



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value208361963419173192001863116334161141623016127128971281012569117801148911200113841071210913105101071697301001099881001972756860597055625225535250095133460244834247458136913596346035553250
Percentage of LiabilitiesAndStockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Stockholders Equity

us-gaap:StockholdersEquity



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-312008-12-312007-12-31
Value502951554843487948804498454444434514410541103844366235963686359935973638365236383145322932563249214420851932170216641658163614721356124312191202114711061011965892738715
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets24.126.325.325.426.227.528.227.428.031.832.130.631.131.332.931.633.633.334.834.032.332.332.632.429.530.432.430.631.931.032.728.729.527.728.726.331.130.829.227.227.50.00.0

Assets Current

us-gaap:AssetsCurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value105279117932895479669811880848365853351705087510744834416421344853939433540204261359438113972444031982875254626022301242923242631222521992088241617491726168918231540
Percentage of AssetsCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets50.546.448.749.751.949.750.251.552.940.139.740.638.138.437.639.436.839.738.239.836.938.139.844.344.041.942.746.844.045.446.451.348.349.149.252.747.448.048.851.347.4

Cash

Cash And Cash Equivalents At Carrying Value

us-gaap:CashAndCashEquivalentsAtCarryingValue



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-12-312009-09-302009-06-302008-12-312007-12-31
Value352604578512871607605652697681564587564545531411425480369321276314290973739298286240224302305282301291241263333249296230227205237226194255
Percentage of CashAndCashEquivalentsAtCarryingValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets1.73.13.02.74.73.73.84.04.35.34.44.74.84.74.73.64.04.43.53.02.83.12.99.710.24.34.84.34.35.66.15.56.66.55.75.79.06.98.66.50.06.30.00.00.00.0

Other Assets Current

us-gaap:OtherAssetsCurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value799107410369938751024951878749708679664594633601605503709700731587666670360289261260203227179182157165188146127117126123111117
Percentage of OtherAssetsCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets3.85.55.45.24.76.35.95.44.65.55.35.35.05.55.45.34.76.56.76.86.06.76.73.64.03.84.43.74.43.43.63.13.64.23.52.83.23.53.63.13.6

Machinery And Equipment Gross

Property Plant And Equipment Gross

Accumulated Depreciation Depletion And Amortization Property Plant And Equipment

Property Plant And Equipment Net

us-gaap:PropertyPlantAndEquipmentNet



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value454467458458450436429427424412413387375377213213218202200198190195196193165160148123108105101100959190877975757980
Percentage of PropertyPlantAndEquipmentNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets2.22.42.42.42.42.72.72.62.63.23.23.13.23.31.91.92.01.91.91.82.02.02.01.92.32.32.52.22.12.02.02.02.12.02.11.92.22.12.22.22.5

Goodwill

us-gaap:Goodwill



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value555556185314524148004625450144034236419741603989389637673762371636933662357935693418344932963027214221451771150614681472137312851195115510921072925883824780742
Percentage of Goodwill100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets26.728.627.727.325.828.327.927.126.332.532.531.733.132.833.632.634.533.634.133.335.134.533.030.229.431.329.727.128.127.527.425.026.025.825.723.425.124.623.821.922.8

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-312009-12-31
Value548855485246519047484573445243584189415241143946386537363734368736643635355235413392342732733005211921221750148414471451135312651174113610741055866732
Percentage of Goodwill98.898.898.799.098.998.998.999.098.998.998.998.999.299.299.299.299.299.399.299.299.399.499.399.399.099.098.898.698.698.698.598.498.398.498.398.498.198.7
Percentage of Assets26.328.327.427.025.528.027.626.926.032.232.131.432.832.533.332.434.233.333.833.134.934.232.830.029.130.929.326.727.727.127.024.625.525.425.323.024.122.5
Percentage of Assets ajg:BrokerageSegment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.039.037.336.638.437.534.336.634.635.332.034.134.033.429.933.831.3

ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-312009-12-31
Value636664484949464243424340282828282827272725222222222221212121202020181817179
Percentage of Goodwill1.11.21.20.91.01.11.01.01.01.01.01.00.70.70.80.80.80.70.80.80.70.60.70.71.01.01.21.41.41.41.51.61.71.61.71.61.91.3
Percentage of Assets0.30.30.30.30.30.30.30.30.30.30.30.30.20.20.30.30.30.30.30.30.30.20.20.20.30.30.40.40.40.40.40.40.40.40.40.40.50.3
Percentage of Assets ajg:RiskManagementSegment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.03.83.93.94.13.94.04.24.33.83.83.93.53.73.33.32.6

us-gaap:Corporate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312012-12-31
Value23332222232222000000000
Percentage of Goodwill0.10.10.10.10.10.10.10.10.10.10.10.10.10.10.00.00.00.00.00.00.00.00.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Percentage of Assets us-gaap:Corporate0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:StatementGeographical

ajg:OtherForeign



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312014-12-31
Value1261311151161121121181181041011038986826948494242
Percentage of Goodwill2.32.32.22.22.32.42.62.72.52.42.52.22.22.21.81.31.31.21.2
Percentage of Assets0.60.70.60.60.60.70.70.70.70.80.80.70.70.70.60.40.50.40.4
Percentage of Assets ajg:OtherForeign0.016.10.00.00.019.00.00.00.022.70.00.00.023.70.00.00.019.118.8

country:AU



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-31
Value36742741441640940641140041441642740541038240039339738034237232433637
Percentage of Goodwill6.67.67.87.98.58.89.19.19.89.910.310.210.510.210.610.610.810.49.610.49.59.81.7
Percentage of Assets1.82.22.22.22.22.52.62.52.63.23.33.23.53.33.63.53.73.53.33.53.33.40.5
Percentage of Assets country:AU0.032.60.00.00.035.60.00.00.037.50.00.00.040.20.00.00.040.00.00.00.052.513.4

country:CA



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-31
Value41845444544643737837336036737534529529329229830229728229331629931826
Percentage of Goodwill7.58.18.48.59.18.28.38.28.78.98.37.47.57.87.98.18.07.78.28.98.89.21.2
Percentage of Assets2.02.32.32.32.32.32.32.22.32.92.72.42.52.52.72.72.82.62.83.03.13.20.4
Percentage of Assets country:CA0.049.60.00.00.048.10.00.00.051.20.00.00.050.70.00.00.048.90.00.00.030.924.6

country:GB



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value1199119011501153793762733739783745745699672666688705749782806828788820833882571597226
Percentage of Goodwill21.621.221.722.016.516.516.316.818.517.817.917.517.217.718.319.020.321.422.523.223.123.825.329.126.727.815.3
Percentage of Assets5.86.16.06.04.34.74.64.64.95.85.85.65.75.86.16.27.07.27.77.78.18.28.38.87.98.74.2
Percentage of Assets country:GB0.023.40.00.00.019.80.00.00.027.50.00.00.028.00.00.00.029.50.00.00.033.50.00.00.031.819.3

country:NZ



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312014-12-31
Value191218206218223219207214224218226224208205216210200204258
Percentage of Goodwill3.43.93.94.24.74.84.64.95.35.25.45.65.45.45.85.75.45.67.5
Percentage of Assets0.91.11.11.11.21.31.31.31.41.71.81.81.81.81.91.91.91.92.6
Percentage of Assets country:NZ0.030.30.00.00.031.00.00.00.030.10.00.00.030.50.00.00.032.642.0

country:US



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value325231962983289128242744265625702341234023112274222521382088205519991970190818071710167215921551150514691177
Percentage of Goodwill58.556.956.155.258.859.359.058.455.355.755.657.057.156.855.555.354.153.853.350.650.048.548.351.270.368.579.9
Percentage of Assets15.616.315.615.115.216.816.515.814.518.118.018.118.918.618.618.118.718.118.216.917.616.715.915.520.721.422.0
Percentage of Assets country:US0.029.60.00.00.029.70.00.00.032.60.00.00.032.60.00.00.033.50.00.00.033.10.00.00.033.232.0

us-gaap:StatementGeographical, us-gaap:StatementBusinessSegments

ajg:OtherForeign, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value12312811211310911011611599
Percentage of Goodwill2.22.32.12.22.32.42.62.62.4
Percentage of Assets0.60.70.60.60.60.70.70.70.8
Percentage of Assets ajg:OtherForeign ajg:BrokerageSegment0.00.00.00.00.00.00.00.00.0

ajg:OtherForeign, us-gaap:Corporate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value233322223
Percentage of Goodwill0.10.10.10.10.10.10.10.10.1
Percentage of Assets0.00.00.00.00.00.00.00.00.0
Percentage of Assets ajg:OtherForeign us-gaap:Corporate0.00.00.00.00.00.00.00.00.0

country:AU, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value358416404415409406411400416
Percentage of Goodwill6.57.47.67.98.58.89.19.19.9
Percentage of Assets1.72.12.12.22.22.52.62.53.2
Percentage of Assets country:AU ajg:BrokerageSegment0.00.00.00.00.00.00.00.00.0

country:AU, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value91010000
Percentage of Goodwill0.20.20.20.00.00.0
Percentage of Assets0.00.10.10.00.00.0
Percentage of Assets country:AU ajg:RiskManagementSegment0.00.00.00.00.00.0

country:CA, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value418454445446437378373360374
Percentage of Goodwill7.58.18.48.59.18.28.38.28.9
Percentage of Assets2.02.32.32.32.32.32.32.22.9
Percentage of Assets country:CA ajg:BrokerageSegment0.00.00.00.00.00.00.00.00.0

country:GB, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value1186117711381144784753726732738
Percentage of Goodwill21.421.021.421.816.316.316.116.617.6
Percentage of Assets5.76.05.96.04.24.64.54.55.7
Percentage of Assets country:GB ajg:BrokerageSegment0.00.00.00.00.00.00.00.00.0

country:GB, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value121212899777
Percentage of Goodwill0.20.20.20.20.20.20.20.20.2
Percentage of Assets0.10.10.10.00.10.10.00.00.1
Percentage of Assets country:GB ajg:RiskManagementSegment0.00.00.00.00.00.00.00.00.0

country:NZ, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value182208196207213209197204209
Percentage of Goodwill3.33.73.74.04.44.54.44.65.0
Percentage of Assets0.91.11.01.11.11.31.21.31.6
Percentage of Assets country:NZ ajg:BrokerageSegment0.00.00.00.00.00.00.00.00.0

country:NZ, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value810910101010109
Percentage of Goodwill0.20.20.20.20.20.20.20.20.2
Percentage of Assets0.00.10.00.10.10.10.10.10.1
Percentage of Assets country:NZ ajg:RiskManagementSegment0.00.00.00.00.00.00.00.00.0

country:US, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value321931632950286127942715262625452280
Percentage of Goodwill58.056.355.554.658.258.758.457.854.3
Percentage of Assets15.516.115.414.915.016.616.315.717.7
Percentage of Assets country:US ajg:BrokerageSegment0.00.00.00.00.00.00.00.00.0

country:US, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-31
Value333333292929292525
Percentage of Goodwill0.60.60.60.60.60.60.70.60.6
Percentage of Assets0.20.20.20.20.20.20.20.20.2
Percentage of Assets country:US ajg:RiskManagementSegment0.00.00.00.00.00.00.00.00.0

Intangible Assets Net Excluding Goodwill

us-gaap:IntangibleAssetsNetExcludingGoodwill



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value22462318207320081841177317721731163916441671166216821627162916591672169817411761172317761771163110931078918784768809722644598561556562489483435431438
Percentage of IntangibleAssetsNetExcludingGoodwill100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets10.811.810.810.59.910.911.010.710.212.813.013.214.314.214.614.615.615.616.616.417.717.717.716.315.015.715.414.114.715.114.412.613.012.513.112.313.313.412.612.113.5

us-gaap:FiniteLivedIntangibleAssetsByMajorClass

ajg:ExpirationLists



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value21552241198919251770170217271685162916331659165016701614161516411651167817201736169317421733160110721052784
Percentage of IntangibleAssetsNetExcludingGoodwill95.996.795.995.896.296.097.597.499.499.399.399.299.399.299.198.998.798.898.898.698.298.197.998.198.097.596.9
Percentage of Assets10.311.410.410.09.510.410.710.410.112.713.013.114.214.114.414.415.415.416.416.217.417.417.416.014.715.314.7
Percentage of Assets ajg:ExpirationLists0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:NoncompeteAgreements



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value1715232310977777877710118810121315106117
Percentage of IntangibleAssetsNetExcludingGoodwill0.80.71.11.10.60.50.40.40.40.40.50.50.40.40.50.60.70.50.50.60.70.80.90.60.61.10.9
Percentage of Assets0.10.10.10.10.10.10.00.00.00.10.10.10.10.10.10.10.10.10.10.10.10.10.20.10.10.20.1
Percentage of Assets us-gaap:NoncompeteAgreements0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:TradeNames



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-31
Value7361606059603637233445681011121417192219151517
Percentage of IntangibleAssetsNetExcludingGoodwill3.32.62.93.03.23.42.12.20.20.20.20.30.30.30.40.50.60.70.70.81.01.11.31.21.41.42.2
Percentage of Assets0.40.30.30.30.30.40.20.20.00.00.00.00.00.00.10.10.10.10.10.10.20.20.20.20.20.20.3
Percentage of Assets us-gaap:TradeNames0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Finite Lived Intangible Assets Net

Deferred Tax Assets Liabilities Net

Other Assets Noncurrent

us-gaap:OtherAssetsNoncurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value674773660670630573584586585567559561536504630606528492480487408385399397383320302270319283245232251235204208204181190186177
Percentage of OtherAssetsNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets3.23.93.43.53.43.53.63.63.64.44.44.54.64.45.65.34.94.54.64.64.23.84.04.05.34.75.14.96.15.34.94.55.55.34.84.65.55.15.55.25.5

Liabilities Current

us-gaap:LiabilitiesCurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value98378921891089328637769374227568774249124705485847844611439843834022419137293905343836423769387530333284257723432215236220902442204420731943228714851577153216891474
Percentage of LiabilitiesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets47.245.446.546.546.447.146.146.648.038.136.738.640.640.139.338.537.538.435.536.435.336.437.738.741.747.943.242.142.444.141.747.644.446.245.849.940.243.944.347.545.4

Other Liabilities Current

Long Term Debt

us-gaap:LineOfCreditFacility, us-gaap:ShortTermDebtType

us-gaap:LongTermDebt

ajg:RentCaptiveFacility, us-gaap:LetterOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value7666666666666666666666666
Percentage of LongTermDebt100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.10.10.10.10.10.10.10.10.10.10.10.10.10.10.1
Percentage of Assets ajg:RentCaptiveFacility us-gaap:LetterOfCredit0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

ajg:SelfInsuranceDeductibles, us-gaap:LetterOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-31
Value99101010999121312121212111111111099999
Percentage of LongTermDebt128.4149.2160.3161.9161.9154.0154.0154.0196.8207.9195.2195.2190.5190.5184.1187.3177.8177.8165.1154.0147.6155.6155.6158.1
Percentage of Assets0.00.00.10.10.10.10.10.10.10.10.10.10.10.10.10.10.10.10.10.10.10.10.10.1
Percentage of Assets ajg:SelfInsuranceDeductibles us-gaap:LetterOfCredit0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:ShortTermDebtType

us-gaap:LetterOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value0001110455555555555555
Percentage of LongTermDebt12.214.314.320.60.020.611.166.779.479.479.479.479.479.479.479.479.479.479.479.479.479.4
Percentage of Assets0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.10.00.10.00.1
Percentage of Assets us-gaap:LetterOfCredit0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Long Term Debt Noncurrent

us-gaap:LongTermDebtNoncurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value4315381638153815369030913141314127922691274126442144214420442344207120752125212521252125212521251425825825925725725725675675675675675675550550550550
Percentage of LongTermDebtNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets20.719.419.919.919.818.919.519.417.320.921.421.018.218.718.320.619.319.020.219.821.821.221.321.219.612.013.816.613.913.514.513.114.715.115.914.718.315.315.915.516.9

Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent

Minority Interest

us-gaap:MinorityInterest



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value40606868777068696959626564595455554955737475
Percentage of MinorityInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.20.30.40.40.40.40.40.40.40.50.50.50.60.50.50.50.50.50.50.70.80.8

Other Liabilities Noncurrent

us-gaap:OtherLiabilitiesNoncurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value122512711127110193790086293193311281191115611231077101510009669589489749471012837769672665635591620605557543526491409417383362367350333
Percentage of OtherLiabilitiesNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets5.96.55.95.75.05.55.35.75.88.79.39.29.59.49.18.89.08.89.09.19.710.18.47.79.29.710.610.611.911.311.110.611.411.09.69.110.410.110.69.910.2

Stockholders Equity

us-gaap:StockholdersEquity



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-312008-12-312007-12-31
Value502951554843487948804498454444434514410541103844366235963686359935973638365236383145322932563249214420851932170216641658163614721356124312191202114711061011965892738715
Percentage of StockholdersEquity100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets24.126.325.325.426.227.528.227.428.031.832.130.631.131.332.931.633.633.334.834.032.332.332.632.429.530.432.430.631.931.032.728.729.527.728.726.331.130.829.227.227.50.00.0

Common Stock Value

us-gaap:CommonStockValue



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value189188186186185184183182182181180180179178177177177176176174166164161159135133131127126125124121118114112112110108106105102
Percentage of CommonStockValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets0.91.01.01.01.01.11.11.11.11.41.41.41.51.61.61.61.71.61.71.61.71.61.61.61.91.92.22.32.42.32.52.42.62.62.72.43.03.03.13.03.2

Retained Earnings Accumulated Deficit

us-gaap:RetainedEarningsAccumulatedDeficit



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value216119011884183918101558151714661426109510621002901916889835753774778710636676683648596596583554506510519500470482480471466488468456450
Percentage of RetainedEarningsAccumulatedDeficit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets10.49.79.89.69.79.59.49.08.88.58.38.07.78.07.97.37.07.17.46.66.56.86.86.58.28.79.810.09.79.510.49.810.210.811.310.312.613.613.512.813.9

Accumulated Other Comprehensive Income Loss Net Of Tax

us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value-1231-759-925-802-721-785-673-651-499-559-498-661-699-763-620-603-535-522-496-338-380-260-83546-2-41-72-55-32-25-48-36-47-12362-2-13-9
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets-5.9-3.9-4.8-4.2-3.9-4.8-4.2-4.0-3.1-4.3-3.9-5.3-5.9-6.6-5.5-5.3-5.0-4.8-4.7-3.2-3.9-2.6-0.80.50.1-0.0-0.7-1.3-1.1-0.6-0.5-0.9-0.8-1.1-0.30.10.20.1-0.1-0.4-0.3

us-gaap:StatementEquityComponents

us-gaap:AccumulatedDefinedBenefitPlansAdjustment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-312011-12-312010-12-31
Value-55-56-57-58-59-61-48-49-43-43-43-44-46-47-38-39-42-42-42-43-43-44-24-24-25-25-52-49-18
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax4.57.46.27.38.37.87.27.68.87.78.76.86.66.26.26.57.98.28.612.811.417.028.9-45.6-368.1984.6159.8103.8-836.4
Percentage of Assets-0.3-0.3-0.3-0.3-0.3-0.4-0.3-0.3-0.3-0.3-0.3-0.4-0.4-0.4-0.3-0.3-0.4-0.4-0.4-0.4-0.4-0.4-0.2-0.2-0.3-0.4-1.0-1.1-0.5
Percentage of Assets us-gaap:AccumulatedDefinedBenefitPlansAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedGainLossNetCashFlowHedgeParent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312016-12-31
Value-119-28-63-38-17-51078-7
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax9.73.76.94.82.40.7-1.5-1.2-1.60.9
Percentage of Assets-0.6-0.1-0.3-0.2-0.1-0.00.10.00.1-0.1
Percentage of Assets us-gaap:AccumulatedGainLossNetCashFlowHedgeParent0.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedOtherComprehensiveIncome



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-312011-12-312010-12-31
Value-1231-759-925-802-721-785-673-651-499-559-498-661-699-763-620-603-535-522-496-338-380-260-83546-2-32-472
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of Assets-5.9-3.9-4.8-4.2-3.9-4.8-4.2-4.0-3.1-4.3-3.9-5.3-5.9-6.6-5.5-5.3-5.0-4.8-4.7-3.2-3.9-2.6-0.80.50.1-0.0-0.6-1.10.1
Percentage of Assets us-gaap:AccumulatedOtherComprehensiveIncome0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:AccumulatedTranslationAdjustment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-312011-12-312010-12-31
Value-1056-674-803-705-644-719-634-609-459-525-459-618-652-709-568-549-490-477-454-301-336-216-5976302220420
Percentage of AccumulatedOtherComprehensiveIncomeLossNetOfTax85.888.886.987.989.391.594.393.691.993.992.293.593.392.991.791.091.591.491.589.088.583.071.6141.3447.8-850.0-62.5-9.3931.8
Percentage of Assets-5.1-3.4-4.2-3.7-3.5-4.4-3.9-3.8-2.8-4.1-3.6-4.9-5.5-6.2-5.1-4.8-4.6-4.4-4.3-2.8-3.5-2.2-0.60.80.40.30.40.10.6
Percentage of Assets us-gaap:AccumulatedTranslationAdjustment0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value108350349515-96260191530-2172613322613076712042251163116-47-73
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 RevenueFromContractWithCustomerExcludingAssessedTax5.820.319.131.1-4.815.710.832.0-11.816.320.92.111.18.38.024.52.97.624.317.9-8.7-1.60.7

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value-105-396-247-591-141-256-208-358-86-108-118-449-1416-44-421-265-132-32-227-72-11-272
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 RevenueFromContractWithCustomerExcludingAssessedTax-5.6-23.0-13.6-35.7-7.1-15.5-11.7-21.6-4.7-6.8-7.5-34.9-120.1-4.9-47.3-31.7-17.0-4.9-33.8-11.1-2.1-6.10.5

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value147981125075-4413269-1-165-2551501409361104129-9261-256911815
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 RevenueFromContractWithCustomerExcludingAssessedTax7.90.60.56.825.50.3-2.58.03.8-0.1-10.4-19.8127.344.840.612.516.6-13.79.1-3.912.726.43.1

Net Cash Provided By Used In Operating Activities

us-gaap:NetCashProvidedByUsedInOperatingActivities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value108350349515-96260191530-2172613322613076712042251163116-47-73
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 RevenueFromContractWithCustomerExcludingAssessedTax5.820.319.131.1-4.815.710.832.0-11.816.320.92.111.18.38.024.52.97.624.317.9-8.7-1.60.7

Net Income Loss

us-gaap:NetIncomeLoss



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value346981261103341171271142731051301301715595122150466213313921519310949607493403361712840464115544644294143
Percentage of NetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax18.55.76.96.616.87.17.26.914.96.68.28.211.53.46.98.310.53.64.79.210.21.84.17.39.25.46.78.912.06.05.09.511.05.17.08.37.63.411.910.09.66.19.59.7

Profit Loss

us-gaap:ProfitLoss



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value355105137121351127138123286113118137180671011301555768140147325410111357
Percentage of ProfitLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:NoncontrollingInterest



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value91111171010812878125751157810
Percentage of ProfitLoss2.68.09.35.08.27.87.14.37.26.34.717.85.85.83.719.78.75.45.632.4

us-gaap:RetainedEarnings



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value3461261103341171271142731051301715595122150466213313921
Percentage of ProfitLoss97.492.090.795.091.892.292.995.792.8110.495.382.294.294.296.380.391.394.694.467.6

Increase Decrease In Other Operating Capital Net

us-gaap:IncreaseDecreaseInOtherOperatingCapitalNet



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value11-3-3227159-5253120-6-928-19-145017-140282159-288649-22302131291110
Percentage of IncreaseDecreaseInOtherOperatingCapitalNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Net Cash Provided By Used In Investing Activities

us-gaap:NetCashProvidedByUsedInInvestingActivities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value-105-396-247-591-141-256-208-358-86-108-118-449-1416-44-421-265-132-32-227-72-11-272
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 RevenueFromContractWithCustomerExcludingAssessedTax-5.6-23.0-13.6-35.7-7.1-15.5-11.7-21.6-4.7-6.8-7.5-34.9-120.1-4.9-47.3-31.7-17.0-4.9-33.8-11.1-2.1-6.10.5

Payments To Acquire Property Plant And Equipment

Net Cash Provided By Used In Financing Activities

us-gaap:NetCashProvidedByUsedInFinancingActivities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value147981125075-4413269-1-165-2551501409361104129-9261-256911815
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 RevenueFromContractWithCustomerExcludingAssessedTax7.90.60.56.825.50.3-2.58.03.8-0.1-10.4-19.8127.344.840.612.516.6-13.79.1-3.912.726.43.1

Proceeds From Issuance Of Long Term Debt

us-gaap:ProceedsFromIssuanceOfLongTermDebt



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302017-12-312017-09-302016-12-312016-09-302014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-31
Value57500125600-5003009810000-100700600000
Percentage of ProceedsFromIssuanceOfLongTermDebt100.00.00.0100.0100.0100.00.0100.0100.0100.00.00.0100.0100.0100.00.00.00.0

Repayments Of Long Term Debt

Payments For Repurchase Of Common Stock

Repayments Of Long Term Debt

Debt Instrument Interest Rate Stated Percentage

Effective Income Tax Rate Continuing Operations

Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-312009-12-312008-12-31
Value9788989991010111110101011889988998889991010101111121313
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PlanName

ajg:LongTermIncentivePlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value222223333444
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber24.435.433.332.230.137.536.336.535.737.737.436.4

Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-312009-12-312008-12-31
Value62.3256.455.9255.5554.9250.1649.9349.4949.3644.9544.8344.6244.3541.441.1840.7940.4239.2539.1638.938.1335.4935.3135.034.5731.3531.2931.1230.7728.828.6228.528.3727.227.1627.1426.7126.2626.2
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

ajg:Range01



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value43.7139.1739.1739.1739.1738.238.0837.9237.8936.1836.1235.9135.6831.5431.3630.9930.7130.5730.5127.2427.2225.7825.8125.8125.8425.8625.8724.8324.4424.2424.2524.1924.02
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice70.169.570.070.571.376.276.376.676.880.580.680.580.576.276.276.076.077.977.970.071.472.673.173.774.782.582.779.879.484.284.784.984.7

ajg:Range02



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value46.4343.7143.7143.7143.7143.7143.7143.7143.7143.7144.7744.7744.7739.1539.1539.1539.1542.9342.9337.6437.6133.1833.0432.6529.7929.7429.7327.5627.4927.026.9426.9326.93
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice74.577.578.278.779.687.187.588.388.697.299.9100.3100.994.695.196.096.9109.4109.696.898.693.593.693.386.294.995.088.689.393.894.194.594.9

ajg:Range03



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value56.8146.4346.4646.4746.4746.4846.4946.4946.4946.5146.9446.9446.8943.7143.7143.7143.7146.8746.8746.1746.1739.1939.1539.1535.6235.4335.430.0430.0329.1229.129.129.1
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice91.282.383.183.784.692.793.193.994.2103.5104.7105.2105.7105.6106.1107.2108.1119.4119.7118.7121.1110.4110.9111.9103.0113.0113.196.597.6101.1101.7102.1102.6

ajg:Range04



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value70.7456.8156.8156.8356.8156.8156.8156.856.856.7856.8656.8656.8646.5346.5346.5346.5347.9247.9246.8846.8746.8746.8746.1639.1735.9535.9535.3835.3533.5133.4431.2433.39
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice113.5100.7101.6102.3103.4113.3113.8114.8115.1126.3126.8127.4128.2112.4113.0114.1115.1122.1122.4120.5122.9132.1132.7131.9113.3114.7114.9113.7114.9116.4116.8109.6117.7

ajg:Range05



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-06-302012-03-31
Value79.5970.7470.7470.7470.7470.7470.7470.7470.7446.8746.8739.1739.1739.1739.1728.835.7135.86
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice127.7125.4126.5127.3128.8141.0141.7142.9143.3133.9135.6124.9125.2125.9127.3100.0125.3126.4

ajg:Range06



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312014-03-312013-12-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-31
Value86.1779.5979.5979.5979.5934.5731.3531.2931.1230.7728.6228.528.37
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice138.3141.1142.3143.3144.9100.0100.0100.0100.0100.0100.0100.0100.0

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period

us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod

us-gaap:RestrictedStockUnitsRSU



Period End2020-03-312019-03-312018-06-302018-03-312017-06-302017-03-312016-03-31
Value405900.0399900.018900.0420200.021600.0477500.0466600.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod100.0100.0100.0100.0100.0100.0100.0

us-gaap:PlanName

ajg:LongTermIncentivePlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-31
Value20002000300300001000200100000
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod542.00.00.00.0700.20.00.00.0832.90.00.016666.783.80.00.00.0214.30.00.00.00.00.00.00.00.00.00.00.00.0

Share Based Compensation

us-gaap:ShareBasedCompensation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value3333333144444333333222222222022101
Percentage of ShareBasedCompensation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Deferred Tax Liabilities

Deferred Tax Assets Net

Unrecognized Tax Benefits

Deferred Tax Assets Valuation Allowance

Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions

Operating Lease Right Of Use Asset

us-gaap:OperatingLeaseRightOfUseAsset



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312019-01-01
Value374393384368368379
Percentage of OperatingLeaseRightOfUseAsset100.0100.0100.0100.0100.0100.0

Cash And Cash Equivalents Period Increase Decrease

Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312015-12-312014-12-31
Value2633262326072546254022362260234421082305218020681822193718921682
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:AmortizationOfDeferredCompensationAndRestrictedStock



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value15121212109912988106678555745664843212111
Percentage of AmortizationOfDeferredCompensationAndRestrictedStock100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitments



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value21-4201901019-30023-12-111337-7795-550-33-37341834
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:GuaranteeObligationsByNature

us-gaap:FinancialGuarantee



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value10001000100020-104-13-101901209
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitments5.7-0.0-3.4100.08.00.0-8.312.59.5-0.0-33.3100.09.70.815.8-0.811.917.6-1.06.839.11.5-3.20.026.1

us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased

ajg:LettersOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value180001801017-3002100021-1002220021000150015
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitments87.116.7-17.2-0.092.0100.0108.387.590.5100.0133.3-0.088.7-0.0-0.0-3.058.02.10.5-0.044.4-5.90.10.060.60.00.00.00.00.00.00.0

us-gaap:OtherCommitments

ajg:FundingCommitments



Period End2020-03-31
Value1
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitments7.1

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFive



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
Value00000000000000000-101000
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFive100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.0100.00.0100.0100.00.0100.0100.0100.00.0

us-gaap:GuaranteeObligationsByNature

us-gaap:FinancialGuarantee



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
Value200000.00.00.00.0200000.00.00.00.0200000.00.00.00.0200000.00.0-200000.00.0400000.0-400000.00.00.0800000.0900000.00.0
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFive100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.0100.00.0100.021.10.00.0100.0100.00.0

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFour



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
Value0000000000000-1100100000
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFour100.00.00.00.0100.00.00.00.0100.00.00.00.0100.0100.0100.00.0100.0100.0100.00.0100.0100.00.0

us-gaap:GuaranteeObligationsByNature

us-gaap:FinancialGuarantee



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
Value200000.00.00.00.0200000.00.00.00.0200000.00.00.00.0200000.00.0-200000.00.0400000.0-300000.0-100000.00.0800000.0800000.00.0
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFour100.00.00.00.0100.00.00.00.0100.00.00.00.0100.0-0.0-18.20.0100.0-25.0100.00.0100.0100.00.0

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearOne



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value1-33-11001000-9-598-3651-56-34-3844181
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearOne100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:GuaranteeObligationsByNature

us-gaap:FinancialGuarantee



Period End2020-03-312019-06-302019-03-312018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value100000.0-100000.0200000.0-100000.0200000.0200000.0-100000.00.0100000.0-200000.0400000.0-300000.00.00.0700000.0800000.00.0
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearOne6.27.113.312.522.215.4100.00.0100.0-2.24.60.80.0-0.011.3-2.3-0.0

us-gaap:OtherCommitments

ajg:FundingCommitments



Period End2020-03-31
Value1
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearOne93.8

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThereafter



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value1800117-11017-4002200023-130-141-211033
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThereafter100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0

us-gaap:GuaranteeObligationsByNature

us-gaap:FinancialGuarantee



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value00000000000010002-120016-41209
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThereafter1.622.2-0.00.03.420.00.00.04.64.2-100.0100.06.160.0-800.0-33.310.088.3350.021.138.6176.9104.30.027.5

us-gaap:LongTermPurchaseCommitmentByCategoryOfItemPurchased

ajg:LettersOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value180011701016-4002100021-1002220021000150015
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThereafter98.477.8100.0100.096.680.0100.00.095.487.5200.0-0.092.1-0.00.0133.390.011.7-250.0-0.054.5-76.9-4.30.063.70.00.00.00.00.00.00.0

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThree



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
Value00000000000000000-320000
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThree100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.0100.0100.0100.0100.0100.00.0100.0100.00.0

us-gaap:GuaranteeObligationsByNature

us-gaap:FinancialGuarantee



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
Value200000.00.00.00.0200000.00.00.00.0200000.00.00.00.0200000.00.0-200000.0-200000.0600000.0-300000.0-100000.00.0800000.0800000.00.0
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThree100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.0100.0100.0100.010.0-3.80.0100.0100.00.0

ajg:AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearTwo



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
Value00000100000000-743-24410000
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearTwo100.00.00.00.0100.0100.00.00.0100.00.00.00.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.00.0

us-gaap:GuaranteeObligationsByNature

us-gaap:FinancialGuarantee



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
Value200000.00.00.00.0200000.00.00.00.0200000.00.00.00.0200000.00.0-200000.0200000.0200000.0-300000.0-100000.00.0800000.0800000.00.0
Percentage of AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearTwo100.00.00.00.0100.00.00.00.0100.00.00.00.0100.0-0.02.84.36.51.2-0.20.0100.0100.00.0

ajg:AmountOfGainLossRecognizedEffectivenessTesting



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value200000.0200000.0300000.0400000.0400000.0
Percentage of AmountOfGainLossRecognizedEffectivenessTesting100.0100.0100.0100.0100.0

us-gaap:IncomeStatementLocation

ajg:CompensationExpense



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value200000.0200000.0300000.0300000.0400000.0
Percentage of AmountOfGainLossRecognizedEffectivenessTesting100.0100.0100.075.0100.0

us-gaap:OperatingExpense



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value200000.0200000.0200000.0300000.0200000.0
Percentage of AmountOfGainLossRecognizedEffectivenessTesting100.0100.066.775.050.0

ajg:BusinessAcquisitionsProFormaNetIncomeLossToControllingInterest



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value34610212710933412212711627310611313017255991221494666134139225596
Percentage of BusinessAcquisitionsProFormaNetIncomeLossToControllingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:BusinessCombinationAggregateEarnoutObligationMaximum



Period End2020-03-312019-12-312019-09-302018-12-312018-09-302018-06-302016-12-312016-09-302016-06-302012-12-312012-09-302012-06-30
Value113021832624955522350350170314289
Percentage of BusinessCombinationAggregateEarnoutObligationMaximum100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:BusinessCombinationAggregateEarnoutObligationRecordedMaximum



Period End2020-03-312019-12-312019-09-302018-12-312018-09-302018-06-302016-12-312016-09-302016-06-302012-12-312012-09-302012-06-30
Value53014526392192661722521225114120
Percentage of BusinessCombinationAggregateEarnoutObligationRecordedMaximum100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AwardType

ajg:CashAndEquityAwardWithAggregateFairValueVestedAndDistributedToParticipants

ajg:DeferredCashParticipationPlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value000103000000000000000
Percentage of CashAndEquityAwardWithAggregateFairValueVestedAndDistributedToParticipants0.00.00.0100.0100.0100.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0

ajg:DeferredEquityParticipationPlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value2011060080000014
Percentage of CashAndEquityAwardWithAggregateFairValueVestedAndDistributedToParticipants0.00.00.076.50.0177.80.00.00.00.00.00.00.00.00.00.0

us-gaap:AwardType

ajg:CashBasedCompensationAwardExpenses

ajg:TwoThousandEighteenProvisionalCashAwards



Period End2020-03-312019-03-312018-03-31
Value210
Percentage of CashBasedCompensationAwardExpenses100.0100.00.0

ajg:TwoThousandSeventeenProvisionalCashAwards



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312017-03-16
Value182222221200000
Percentage of CashBasedCompensationAwardExpenses726.90.00.00.0126.30.00.00.00.00.00.00.00.00.0

ajg:TwoThousandTwentyProvisionalCashAwards



Period End2020-03-31
Value2
Percentage of CashBasedCompensationAwardExpenses84.6

us-gaap:TitleOfIndividual, us-gaap:AwardType

srt:Officer, ajg:CashAwards



Period End2020-03-31
Value0.0
Percentage of CashBasedCompensationAwardExpenses0.0

ajg:ChangeInEstimatedAcquisitionEarnoutPayables



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value-89353225-6731010511104133149510047500-2423-52-4-20-30111
Percentage of ChangeInEstimatedAcquisitionEarnoutPayables100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AwardType

ajg:CompensationApprovedByCommitteeValue

ajg:DeferredCashParticipationPlan



Period End2020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-06-302017-03-312016-06-302016-03-312016-03-312015-03-312014-03-312013-03-31
Value322255555353222
Percentage of CompensationApprovedByCommitteeValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:DeferredEquityParticipationPlan



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-03-312015-03-312014-03-31
Value14101010110011140014101089
Percentage of CompensationApprovedByCommitteeValue470.0420.8420.8420.80.00.00.0205.40.00.00.0274.50.0198.0329.6317.2

ajg:DeferredEquityParticipationPlanSubPlans



Period End2020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-06-302017-03-312016-06-30
Value122200000413
Percentage of CompensationApprovedByCommitteeValue60.0108.3108.3108.30.00.016.10.00.078.4438.7

ajg:ContractWithCustomerImpactOfChangeInForeignExchangeRates



Period End2020-03-31
Value17
Percentage of ContractWithCustomerImpactOfChangeInForeignExchangeRates100.0

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-31
Value17
Percentage of ContractWithCustomerImpactOfChangeInForeignExchangeRates100.0

ajg:ContractWithCustomerLiabilityAdditions



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value2086437106204
Percentage of ContractWithCustomerLiabilityAdditions100.0100.0100.0100.0100.0

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value16637471162
Percentage of ContractWithCustomerLiabilityAdditions79.757.313.266.979.6

ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value4227323541
Percentage of ContractWithCustomerLiabilityAdditions20.342.786.833.120.4

ajg:CostReimbursements



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value37373433333437353433333533
Percentage of CostReimbursements100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:DeferredCompensationAndRestrictedStockExpensesBenefit



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value15114-79812-148810-2266-4-8
Percentage of DeferredCompensationAndRestrictedStockExpensesBenefit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value15114-79812-148810-2266-4-8
Percentage of DeferredCompensationAndRestrictedStockExpensesBenefit102.0100.097.6100.0100.098.8100.0101.4100.0100.099.1100.9100.0100.0100.0102.4

us-gaap:CommonStock



Period End2020-03-312019-06-302018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value-300000.0100000.00.0100000.00.0200000.00.00.0100000.0200000.00.00.00.0200000.0
Percentage of DeferredCompensationAndRestrictedStockExpensesBenefit-2.02.40.01.20.0-1.40.00.00.9-0.90.00.0-0.0-2.4

ajg:EarnoutPaymentsForAcquisitions



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value21823585311591141510311227
Percentage of EarnoutPaymentsForAcquisitions100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Range, us-gaap:BusinessAcquisition, us-gaap:ValuationTechnique

ajg:FairValueInputsAttritionRate

srt:Maximum, ajg:TwoThousandSeventeenAcquisitions, us-gaap:IncomeApproachValuationTechnique



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302017-09-30
Value0.1410.00.06-0.075999999999999980.1410.0099999999999999950.00.0
Percentage of FairValueInputsAttritionRate100.00.0100.0100.0100.0100.00.00.0

srt:Minimum, ajg:TwoThousandSeventeenAcquisitions, us-gaap:IncomeApproachValuationTechnique



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302017-09-30
Value0.050.00.00.00.05-0.0150.00.0
Percentage of FairValueInputsAttritionRate35.50.00.0-0.035.5-150.00.00.0

ajg:IncreaseDecreaseInPremiumsAndFeeReceivable



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-30
Value2055-397-276-17612850-315-4081505-752-734
Percentage of IncreaseDecreaseInPremiumsAndFeeReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:NetBorrowingsOnPremiumFinancingDebtFacility



Period End2020-03-312019-12-312019-03-312018-12-31
Value-26-4-2013
Percentage of NetBorrowingsOnPremiumFinancingDebtFacility100.0100.0100.0100.0

ajg:NetChangeInAccruedCompensationAndOtherAccruedLiabilities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value307-127-116-41209-101-79-29165-100-46120-43-141-10101-19-180-2727-38-72-5857-11113-5648-41-61-26906458
Percentage of NetChangeInAccruedCompensationAndOtherAccruedLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:NetProceedsFromSalesOfOperations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-12-312011-09-302011-03-31
Value112374109200110411043050022020204101
Percentage of NetProceedsFromSalesOfOperations100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:PaymentsToAcquireBusinessesNetOfCashAndRestrictedCashAcquired



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value7631521755817520918033857738877137
Percentage of PaymentsToAcquireBusinessesNetOfCashAndRestrictedCashAcquired100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:RecordedEarnOutPayable



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value1321023796354121171331181732196153133291128281762617232927
Percentage of RecordedEarnOutPayable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:RevenueFromContractWithCustomerBeforeReimbursementsExcludingAssessedTax



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value182916831790162419571623174116251802148515591454
Percentage of RevenueFromContractWithCustomerBeforeReimbursementsExcludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value143511921195113113811001104910001195895938896
Percentage of RevenueFromContractWithCustomerBeforeReimbursementsExcludingAssessedTax78.570.866.869.670.661.760.361.566.360.360.261.6

us-gaap:OperatingSegments, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value211214211209203202199201195188190181
Percentage of RevenueFromContractWithCustomerBeforeReimbursementsExcludingAssessedTax11.612.711.812.910.412.511.412.410.812.712.212.5

us-gaap:OperatingSegments, us-gaap:Corporate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value181276383284372419492423412401430376
Percentage of RevenueFromContractWithCustomerBeforeReimbursementsExcludingAssessedTax9.916.421.417.519.025.828.326.022.927.027.625.9

us-gaap:AwardType

ajg:ShareBasedCompensationArrangementByShareBasedPaymentAwardAggregateFairValue

us-gaap:PerformanceShares



Period End2020-03-122019-03-142019-03-142018-09-302018-06-302018-03-152018-03-312017-09-302017-06-302017-03-162017-03-312016-03-172016-03-112015-03-112014-03-12
Value755005500443322
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardAggregateFairValue100.0100.00.00.0100.0100.00.00.0100.0100.0100.0100.0100.0100.0

us-gaap:AwardType

ajg:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue

us-gaap:RestrictedStockUnitsRSU



Period End2020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-06-302017-03-312016-03-31
Value343131312812812620
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-30
Value25171220277134294561646610312103610935
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AwardType

ajg:UnearnedDeferredCompensationShare

ajg:DeferredEquityParticipationPlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value20002254542002200
Percentage of UnearnedDeferredCompensationShare100.00.00.00.0100.0100.0100.0100.0100.00.0100.0100.00.0100.0

us-gaap:AwardType

ajg:UnearnedDeferredCompensationValue

ajg:DeferredEquityParticipationPlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value76-4-346960626754-3-3266-2-2
Percentage of UnearnedDeferredCompensationValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:WeightedAverageNumberOfCommonAndCommonEquivalentSharesOutstanding



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value19301901891880186185185018218218118001781781771176171166316115513511311281271124121117113111110105104
Percentage of WeightedAverageNumberOfCommonAndCommonEquivalentSharesOutstanding100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AdjustmentForAmortization



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value1359384797676727368656969656462636259685859545454423835302929252526212018161416131314
Percentage of AdjustmentForAmortization100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AwardType

us-gaap:AllocatedShareBasedCompensationExpense

ajg:DeferredCashParticipationPlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-09-302013-06-302013-03-31
Value111110010000000000000000000000
Percentage of AllocatedShareBasedCompensationExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:DeferredEquityParticipationPlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-30
Value222222221222312221222
Percentage of AllocatedShareBasedCompensationExpense135.3152.9216.7216.7181.8800.0266.7240.0237.5371.4371.4428.6450.0500.0525.0600.0350.01000.0700.01050.0

ajg:DeferredEquityParticipationPlanSubPlans



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-30
Value700000.0600000.0600000.0700000.0500000.0500000.0600000.0600000.0500000.0500000.0500000.0500000.0500000.0400000.0500000.0400000.0400000.0
Percentage of AllocatedShareBasedCompensationExpense41.235.350.058.345.5166.766.760.062.571.471.471.4100.0125.0100.0100.0

us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount



Period End2020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-09-302017-09-302017-06-302017-03-312016-09-302016-06-30
Value0011110111046
Percentage of AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312012-09-302012-03-31
Value010000000000000000131211013-554955511
Percentage of BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisitionProFormaEarningsPerShareBasic



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value1.830.520.680.591.810.66999999999999990.70.641.510.58000000000000010.620.720.960.310.55999999999999980.690.840.260.37000000000000010.760.810.130.250.590.710.370.510.570.730.320.309999999999999830.50.590.240.420.360.150.460.44
Percentage of BusinessAcquisitionProFormaEarningsPerShareBasic100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisitionProFormaEarningsPerShareDiluted



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value1.790.50999999999999980.670.571.770.64999999999999990.680.631.480.58000000000000010.620.710.950.310.560.690.840.260.36999999999999990.760.80.130.250.580.70.360.50000000000000020.570.730.320.29999999999999980.490.590.240.420.360.150.460.44
Percentage of BusinessAcquisitionProFormaEarningsPerShareDiluted100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisitionsProFormaNetIncomeLoss



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value995122111025805-50-6-230-9010616-30313351017064152
Percentage of BusinessAcquisitionsProFormaNetIncomeLoss100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisitionsProFormaRevenue



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value1868181318351672199317391780168318391622165015891566141414201482142913041377146113791234130312931251916107585077967474765365455047404554946
Percentage of BusinessAcquisitionsProFormaRevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:BusinessAcquisition



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value614072431869612064331221434221425240215167161822
Percentage of BusinessAcquisitionsProFormaRevenue0.37.73.92.60.94.03.51.20.32.71.91.41.02.41.51.00.23.82.81.50.512.812.56.60.2

us-gaap:BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-262018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value62107653533424123150138020371747714948
Percentage of BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:CapsicumReinsuranceBrokersLLP



Period End2020-03-31
Value62
Percentage of BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable100.0

us-gaap:BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1



Period End2020-03-312019-12-312019-03-312018-12-31
Value-1-1-7-1
Percentage of BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1100.0100.0100.0100.0

us-gaap:BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value1087554445544554444434433333222222221211
Percentage of BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value916605304-23-84236-196124111246-115
Percentage of CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CommonStockDividendsPerShareDeclared



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value0.450.429999999999999940.430.430.430.40999999999999990.410.410.410.39000000000000010.390.390.390.390.38000000000000010.380.380.380.36999999999999990.370.370.370.35999999999999990.360.360.360.349999999999999870.350.350.350.34000000000000010.340.340.340.330.330.330.320.320.320.320.32
Percentage of CommonStockDividendsPerShareDeclared100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ComprehensiveIncomeNetOfTax



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value-1262606293974105-3133443273293209120-4810679300-38205-97-125-4415658991057518268459393038195639
Percentage of ComprehensiveIncomeNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value101071118111131485581366814921-1-4311-10
Percentage of ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value-116270144041615116-2834851279299218133-4211387459-16203-101-146-3616167
Percentage of ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ContractWithCustomerLiabilityIncreaseDecreaseForContractAcquiredInBusinessCombination



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value164200
Percentage of ContractWithCustomerLiabilityIncreaseDecreaseForContractAcquiredInBusinessCombination100.0100.0100.0100.0100.0

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value164200
Percentage of ContractWithCustomerLiabilityIncreaseDecreaseForContractAcquiredInBusinessCombination100.0100.0100.0100.0100.0

us-gaap:ContractWithCustomerLiabilityRevenueRecognized



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value2046151103181
Percentage of ContractWithCustomerLiabilityRevenueRecognized100.0100.0100.0100.0100.0

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value154331567137
Percentage of ContractWithCustomerLiabilityRevenueRecognized75.654.630.365.775.7

ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value5027363544
Percentage of ContractWithCustomerLiabilityRevenueRecognized24.445.469.734.324.3

us-gaap:CostOfGoodsAndServicesSold



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-30
Value185280397292382434508441431309291326270171155146765837272917011
Percentage of CostOfGoodsAndServicesSold100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CostOfRevenue



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-30
Value185280397292382434508441431309291326270171155146765837272917011
Percentage of CostOfRevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CostsAndExpenses



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-30
Value1510163717101552166816141688155615951516151614871416136013161387128912441306134912421200121511911067
Percentage of CostsAndExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Depreciation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value363635353433333030303030302927252624252322211918161415141310101010999888777
Percentage of Depreciation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DepreciationAmortizationAndAccretionNet



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value17212911911511010910610498961009593898888849381827673725952504542403636302421
Percentage of DepreciationAmortizationAndAccretionNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value-1-2-1-1011110-1-1-2-3-30-1
Percentage of DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeInstrumentRisk, us-gaap:IncomeStatementLocation

us-gaap:ForeignExchangeContract, ajg:CommissionRevenue



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value0-10000000-1-2-2-2-3-30-1
Percentage of DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet33.354.518.28.314.353.336.430.838.9-220.0143.8147.1116.7113.3109.1128.6100.0

us-gaap:InterestRateContract, us-gaap:InterestExpense



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value-300000.0-300000.0-300000.0-300000.0-300000.0300000.0300000.0300000.0200000.0
Percentage of DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet25.013.627.325.042.920.027.323.111.1

us-gaap:IncomeStatementLocation

ajg:CompensationExpense



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value-300000.0-400000.0-400000.0-400000.0-200000.0200000.0200000.0400000.0500000.0700000.0400000.0500000.0200000.0200000.0200000.0
Percentage of DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet25.018.236.433.328.613.318.230.827.8140.0-25.0-29.4-8.3-6.7-6.1

us-gaap:OperatingExpense



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value-200000.0-300000.0-200000.0-400000.0-100000.0200000.0200000.0200000.0400000.0500000.0300000.0300000.0200000.0100000.0100000.0
Percentage of DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet16.713.618.233.314.313.318.215.422.2100.0-18.8-17.6-8.3-3.3-3.0

us-gaap:DividendsCommonStockCash



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value86818180767675757171707068686867666564615958574846464544422064036
Percentage of DividendsCommonStockCash100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:RetainedEarnings



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value86818180767675757171707068686867666564615958574846464544422064036
Percentage of DividendsCommonStockCash100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value-14253-49-3134-32-22-6838-26631519
Percentage of EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ForeignCurrencyTransactionGainLossUnrealized



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-30
Value12-31-1-2002-11-31-14-210000000000000-100000
Percentage of ForeignCurrencyTransactionGainLossUnrealized100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LineOfCreditFacility, us-gaap:SubsequentEventType

us-gaap:GainLossOnDerivativeInstrumentsNetPretax

ajg:NotePurchaseAgreement, us-gaap:SubsequentEvent



Period End2020-01-30
Value8
Percentage of GainLossOnDerivativeInstrumentsNetPretax100.0

us-gaap:GainLossOnInvestments



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-03-312010-03-31
Value01301570052-1011110203300-13210529200004
Percentage of GainLossOnInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0

us-gaap:GoodwillAcquiredDuringPeriod



Period End2020-03-312019-03-312018-03-312017-03-312016-03-312015-03-312014-03-312013-03-312012-03-31
Value1591314191334320535
Percentage of GoodwillAcquiredDuringPeriod100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-312019-03-312018-03-312017-03-312016-03-312015-03-312014-03-312013-03-312012-03-31
Value1591313891334320535
Percentage of GoodwillAcquiredDuringPeriod100.0100.093.4100.0100.0100.0100.0100.0100.0

us-gaap:GoodwillPurchaseAccountingAdjustments



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value19-1888-1100001311010-9229218-23-280003-110
Percentage of GoodwillPurchaseAccountingAdjustments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.0100.0100.0100.0100.0100.0

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value181-1888-110100131101-1-9229218-23-280003-110
Percentage of GoodwillPurchaseAccountingAdjustments94.30.098.9103.5100.0100.0100.0100.0-475.0100.0100.0100.0100.0100.0100.0100.0-433.3100.0100.0100.0100.0100.0100.0100.0100.00.00.0100.0100.075.075.0100.0

ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302018-12-312018-09-302018-06-302018-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302012-12-312012-09-30
Value100000-2000100000000
Percentage of GoodwillPurchaseAccountingAdjustments5.70.01.1-0.00.00.0575.00.0-0.00.0533.3-0.00.00.00.00.0-0.025.025.0

us-gaap:GoodwillTranslationAndPurchaseAccountingAdjustments



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value-24182-60-3942-54-14-8630-39981635-74-10-35-3-16-9422-78-90-74246814-3213095
Percentage of GoodwillTranslationAndPurchaseAccountingAdjustments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value-23781-59-3941-54-13-8530-38971635-74-10-35-3-15-9421-78-90-74236814-3213095
Percentage of GoodwillTranslationAndPurchaseAccountingAdjustments98.398.499.098.298.8100.295.098.798.499.299.598.299.799.699.199.297.099.499.999.599.999.7100.099.6100.098.999.399.499.3100.098.9100.0

ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302013-06-302013-03-312012-12-31
Value-3100000-10000000000000000
Percentage of GoodwillTranslationAndPurchaseAccountingAdjustments1.61.71.01.81.2-0.03.61.21.91.00.50.40.90.83.00.60.10.50.10.3-0.00.60.70.0

us-gaap:Corporate



Period End2020-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value-200000.0100000.0-200000.0-100000.0-100000.0100000.00.00.0100000.00.00.00.00.00.00.0
Percentage of GoodwillTranslationAndPurchaseAccountingAdjustments0.1-0.21.40.1-0.3-0.30.00.00.3-0.0-0.00.0-0.0-0.0-0.0

us-gaap:StatementBusinessSegments

us-gaap:ImpairmentOfIntangibleAssetsFinitelived

ajg:BrokerageSegment



Period End2020-03-312019-03-31
Value450
Percentage of ImpairmentOfIntangibleAssetsFinitelived100.00.0

us-gaap:IncomeTaxesPaidNet



Period End2020-03-312019-03-312018-12-312018-09-302017-12-312017-09-30
Value29-11710610
Percentage of IncomeTaxesPaidNet100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInAccruedIncomeTaxesPayable



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value2300-2935-511-1116210-5-5-1612-3-3-614-8-18-156-5-565-21-3-1-43
Percentage of IncreaseDecreaseInAccruedIncomeTaxesPayable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInContractWithCustomerLiability



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value4-4-9818-140329
Percentage of IncreaseDecreaseInContractWithCustomerLiability100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInDeferredIncomeTaxes



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value3712442567472270755060551734614516495752250293016171018723-2-2-3-5
Percentage of IncreaseDecreaseInDeferredIncomeTaxes100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInOtherOperatingAssets



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value-206535783-1335777118-11923773-56262111-85-97120-8427663620-1447-2751-4024-27-1310
Percentage of IncreaseDecreaseInOtherOperatingAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncreaseDecreaseInReinsurancePayables



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value1863-381-23520287690-377127979135-246475-30264-385587-114187-105405-8121-5239-195121-178206-3588-40511-53-25
Percentage of IncreaseDecreaseInReinsurancePayables100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:IncrementalCommonSharesAttributableToShareBasedPaymentArrangements



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value404430333022110000001101110111011100100
Percentage of IncrementalCommonSharesAttributableToShareBasedPaymentArrangements100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:InterestPaid



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value4549444529403237283428313030282529222823282231819817517416161312
Percentage of InterestPaid100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LaborAndRelatedExpense



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value896857838806837760765724775738680680675657659626631622633604615575606564530466473412415383411373364344341324295280275262263270
Percentage of LaborAndRelatedExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value1881311101088987810778
Percentage of MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:NoncontrollingInterest



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-31
Value1881311101088987810778
Percentage of MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:MinorityInterestDecreaseFromRedemptions



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-30
Value1007002-210
Percentage of MinorityInterestDecreaseFromRedemptions100.0100.0100.0100.0100.0100.0100.0100.00.0

us-gaap:StatementEquityComponents

us-gaap:NoncontrollingInterest



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-30
Value10070-12-410
Percentage of MinorityInterestDecreaseFromRedemptions100.0100.0100.033.3-237.575.0155.2100.00.0

us-gaap:NetIncomeLossAttributableToNoncontrollingInterest



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value97111117101081287781257511578103748
Percentage of NetIncomeLossAttributableToNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LineOfCreditFacility, us-gaap:LongtermDebtType, us-gaap:SubsequentEventType, us-gaap:SubsidiarySaleOfStock

us-gaap:NotesIssued1

ajg:NotePurchaseAgreement, ajg:UnsecuredNotes, us-gaap:SubsequentEvent, us-gaap:PrivatePlacement



Period End2020-01-30
Value575
Percentage of NotesIssued1100.0

us-gaap:NumberOfBusinessesAcquired



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-30
Value75.030.029.046.033.017.038.049.039.019.031.031.046.040.024.027.027.032.033.035.024.024.018.017.018.021.026.020.023.017.015.012.013.06.08.04.03.09.0
Percentage of NumberOfBusinessesAcquired100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:NumberOfReportableSegments



Period End2020-03-312019-12-312019-09-30
Value3.00.00.0
Percentage of NumberOfReportableSegments100.00.00.0

us-gaap:OperatingExpenses



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value257280268257262237227222216226209214211200199189204204222208207203221205184157147133137133129121123108113108948487818379
Percentage of OperatingExpenses100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value-381128-98-6074-84-25-15062-661571573358-140-19-59-12-23-15249-134-156-1364581129-15-23-119-1210-16-3410-4
Percentage of OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTaxParent



Period End2020-03-312019-03-31
Value-91-11
Percentage of OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTaxParent100.0100.0

us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome



Period End2020-03-312019-03-31
Value-91-11
Percentage of OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTaxParent100.0100.0

us-gaap:OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax



Period End2020-03-312019-03-31
Value-121-17
Percentage of OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax100.0100.0

us-gaap:DerivativeInstrumentRisk, us-gaap:IncomeStatementLocation

us-gaap:ForeignExchangeContract, ajg:CommissionRevenue



Period End2020-03-312019-03-31
Value-193
Percentage of OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax15.9-21.5

us-gaap:InterestRateContract, us-gaap:InterestExpense



Period End2020-03-312019-03-31
Value-102-20
Percentage of OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax84.1121.5

us-gaap:OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value-380-101-6075-83-24-15064-651573358-140-20-56-9-19-138
Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value-381-98-6074-84-25-14462-651593356-140-19-59-12-23-152
Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax100.397.099.799.2101.2101.296.396.6100.8101.098.897.3100.295.1104.2128.3119.6110.1

us-gaap:NoncontrollingInterest



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-30
Value1-30010-5-20-1010-122314
Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax-0.33.00.30.8-1.2-1.23.7-3.4-0.8-1.01.22.7-0.24.9-4.2-28.3-19.6-10.1

us-gaap:TradingActivityByType

us-gaap:ForeignExchange



Period End2020-03-312019-12-312019-09-302019-06-302019-03-31
Value300000.0-100000.00.0200000.0100000.0
Percentage of OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax-0.10.0-0.0-0.30.1

us-gaap:StatementEquityComponents

us-gaap:OtherComprehensiveIncomeLossNetOfTax

us-gaap:AccumulatedDefinedBenefitPlansAdjustment



Period End2020-03-31
Value1
Percentage of OtherComprehensiveIncomeLossNetOfTax100.0

us-gaap:AccumulatedGainLossNetCashFlowHedgeParent



Period End2020-03-31
Value-91
Percentage of OtherComprehensiveIncomeLossNetOfTax-7616.7

us-gaap:AccumulatedOtherComprehensiveIncome



Period End2020-03-31
Value-471
Percentage of OtherComprehensiveIncomeLossNetOfTax-39291.7

us-gaap:AccumulatedTranslationAdjustment



Period End2020-03-31
Value-381
Percentage of OtherComprehensiveIncomeLossNetOfTax-31775.0

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value-1-1-10-11205-70-1-1-1-180-20000020000-2600-111212900
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value-1-10-11200-70-1-1-180-20000020000-2600-111
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax100.0100.0100.0100.0100.0100.0-10.9100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax



Period End2020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value0001034
Percentage of OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value18-1-20111110-1-1-2-800000000000000000
Percentage of OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.00.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value1111111110111-911111111200013-91212
Percentage of OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax



Period End2020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-31
Value-28-874001
Percentage of OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsForCapitalImprovements



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-31
Value2931323639332831313528362979
Percentage of PaymentsForCapitalImprovements100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsForProceedsFromInvestments



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-30
Value051000150-10021591056813610016341213592
Percentage of PaymentsForProceedsFromInvestments100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsOfDebtIssuanceCosts



Period End2020-03-312019-03-31
Value10
Percentage of PaymentsOfDebtIssuanceCosts100.0100.0

us-gaap:PaymentsOfDividendsCommonStock



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value87818080797575747671707071676767686567626258585649464545448441383432
Percentage of PaymentsOfDividendsCommonStock100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsToAcquireBusinessesGross



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-012016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-30
Value14331021457217623113636162728571143107451474110995202477442138013428201
Percentage of PaymentsToAcquireBusinessesGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PaymentsToMinorityShareholders



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value74359191023813881077915889109109988
Percentage of PaymentsToMinorityShareholders100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromIssuanceOfCommonStock



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-312010-03-31
Value2318183232122215321015142081514641017018361292918111324272112262612
Percentage of ProceedsFromIssuanceOfCommonStock100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ProceedsFromLinesOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value17301580735975102578049099081542011131155955112059769033231527124617921475033674452172101814105157
Percentage of ProceedsFromLinesOfCredit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0

us-gaap:RepaymentsOfLinesOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value1970145067091010306454951215645305135612328381100574761221273273206429915371753050822609712484975
Percentage of RepaymentsOfLinesOfCredit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AwardType

us-gaap:RestrictedStockExpense

us-gaap:RestrictedStockUnitsRSU



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-30
Value107786668644464446
Percentage of RestrictedStockExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302010-03-312009-09-302009-06-30
Value1866172118251657199016571778166018371599159315841489164613851482142713001334145413711231124512861179915890835779674673650649546578562546447459463459482439453
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ConsolidationItems, us-gaap:ProductOrService, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ajg:BrokerFees, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value295277278256261231253220253195225205
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax15.816.115.315.413.213.914.313.313.812.214.213.8

us-gaap:OperatingSegments, ajg:BrokerFees, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value211214211208202202199201194188190181
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax11.312.411.612.610.212.211.212.210.611.812.012.2

us-gaap:OperatingSegments, ajg:Commissions, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1017792809777940685707688839624637618
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax54.546.044.446.947.241.439.841.445.739.040.041.5

us-gaap:OperatingSegments, ajg:ContingentRevenue, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value452730294815252134212121
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.41.61.71.82.40.91.41.31.91.31.41.4

us-gaap:OperatingSegments, ajg:NetGainsOnDivestitures, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value01331570062
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.00.80.20.12.90.00.00.40.2

us-gaap:OperatingSegments, ajg:Reimbursements, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value373734333334373534333335
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.02.21.92.01.72.12.12.11.92.12.12.4

us-gaap:OperatingSegments, ajg:SupplementalRevenueMember, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value595749465645434852383635
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax3.23.32.72.82.82.82.52.92.82.42.32.4

us-gaap:OperatingSegments, us-gaap:InvestmentPerformance, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value182423191722171513151514
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.01.41.31.20.91.41.00.90.71.01.01.0

us-gaap:OperatingSegments, us-gaap:InvestmentPerformance, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value300000.0300000.0400000.0500000.0400000.0100000.0100000.0100000.0200000.0200000.0100000.0200000.0
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.00.00.00.00.00.00.00.00.00.00.00.0

us-gaap:OperatingSegments, us-gaap:PublicUtilitiesInventoryCoal, us-gaap:Corporate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value181276386284372419492422412401430376
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax9.716.121.117.218.725.327.725.422.425.127.025.3

us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value143511921195113113811001104910001195895938953896878859877939825851835885751816795737564
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax76.969.365.568.269.460.459.060.265.156.058.960.253.462.159.265.863.563.857.464.661.065.661.862.661.7

us-gaap:OperatingSegments, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value249252246242236236236237229222224200216182297176176179181179189177154172172164
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax13.414.713.514.611.914.313.314.312.513.914.114.611.121.511.912.413.813.612.313.814.412.413.414.717.9

us-gaap:OperatingSegments, us-gaap:Corporate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-31
Value181276383284372419492423412401430430376351313428311295301440296303274318268186
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax9.716.121.017.218.725.327.725.522.425.127.025.321.422.628.921.822.722.630.321.624.622.024.822.820.4

us-gaap:ConsolidationItems, us-gaap:StatementGeographical, us-gaap:StatementBusinessSegments

us-gaap:OperatingSegments, ajg:OtherForeign, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value4753363838423139342733
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.63.12.02.31.92.61.82.42.21.72.3

us-gaap:OperatingSegments, country:AU, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value4353525846494953485052
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.33.12.93.52.33.02.83.23.03.23.5

us-gaap:OperatingSegments, country:AU, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value2122222022242125211919
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.21.31.21.21.11.51.21.51.31.21.3

us-gaap:OperatingSegments, country:CA, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value5653525857504047453536
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax3.03.12.93.52.93.02.32.92.82.22.5

us-gaap:OperatingSegments, country:CA, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value11111101110
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.10.10.10.10.10.10.10.10.10.10.1

us-gaap:OperatingSegments, country:GB, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value254247221248203173169204164168184
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax13.614.412.215.010.210.59.512.310.310.612.4

us-gaap:OperatingSegments, country:GB, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value1111101010888887
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.60.60.60.60.50.50.50.50.50.50.5

us-gaap:OperatingSegments, country:NZ, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value2837364130373539343636
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.52.22.02.51.52.22.02.42.22.32.5

us-gaap:OperatingSegments, country:NZ, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value23344344454
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.10.20.20.20.20.20.20.30.30.30.3

us-gaap:OperatingSegments, country:US, ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value10057467956851006648724615568620552
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax53.943.443.641.350.639.140.737.135.538.937.1

us-gaap:OperatingSegments, country:US, ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value212214208206198198201197186190185
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax11.412.511.412.510.012.011.311.911.712.012.4

us-gaap:OperatingSegments, country:US, us-gaap:Corporate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-30
Value181276383284372419492423401430376
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax9.716.121.017.218.725.327.725.525.127.025.3

us-gaap:ProductOrService

ajg:BrokerFees



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value507491490464464433452422448383416386
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax27.228.626.928.023.326.125.525.424.424.026.126.0

ajg:Commissions



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value1017792809777940685707688839624637618
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax54.546.044.446.947.241.439.841.445.739.040.041.5

ajg:ContingentRevenue



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value452730294815252134212121
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.41.61.71.82.40.91.41.31.91.31.41.4

ajg:GainsOnDivestitures



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value01331570062
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.00.80.20.12.90.00.00.40.2

ajg:NetGainsOnDivestitures



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value01331570062
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax0.00.80.20.12.90.00.00.40.2

ajg:Reimbursements



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value373734333334373534333335
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.02.21.92.01.72.12.12.11.92.12.12.4

ajg:SupplementalRevenueMember



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value595749465645434852383635
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax3.23.32.72.82.82.82.52.92.82.42.32.4

us-gaap:InvestmentPerformance



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value182524191822181513161514
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.01.51.31.20.91.41.01.00.71.01.01.0

us-gaap:PublicUtilitiesInventoryCoal



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-30
Value181276386284372419492422412401430376
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax9.716.121.117.218.725.327.725.422.425.127.025.3

us-gaap:StatementGeographical

ajg:OtherForeign



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value47533638384231393534273331
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax2.63.12.02.31.92.61.82.41.92.21.72.31.9

country:AU



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value64757578687370796769697159
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax3.54.44.14.83.44.43.94.83.74.44.44.83.6

country:CA



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value57545359585141494346363732
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax3.13.22.93.62.93.12.33.02.42.92.32.52.0

country:GB



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value265258232258213182178213200173177191167
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax14.215.012.715.610.711.010.012.810.910.811.112.910.2

country:NZ



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value30413945344139433338414128
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax1.62.42.22.71.72.52.22.61.82.42.62.81.7

country:US



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value1400123713871176157712651418123514571156124111141327
Percentage of RevenueFromContractWithCustomerExcludingAssessedTax75.071.976.071.079.276.479.874.479.372.377.974.880.6

us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue

ajg:UnvestedRestrictedStock



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value29002010121
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue100.0100.00.0100.00.0100.00.0100.0100.0

us-gaap:PerformanceShares



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value12000500030002
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue41.90.00.00.00.00.00.00.017.50.00.00.00.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value0.0180.00.00.00.0170.00.00.00.0230.00.00.00.0280.00.00.00.030.00.00.00.030.00.00.00.030.00.00.00.0350.00.00.040.045
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.0100.0100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value0.1730.00.00.00.1560.00.00.00.1510.00.00.00.2720.00.00.00.2770.00.00.00.2820.00.00.00.2890.00.00.00.2960.00.00200000000000000180.2670.268
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.0100.0100.0100.0

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value0.0070.00.00.00.0250.00.00.00.0270.00.00.00.0230.00.00.00.0160.00.00.00.0180.00.00.00.0180.00.00.00.0120.00.00.0120.027
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.0100.0100.0

us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue

ajg:DeferredEquityParticipationPlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-30
Value23517430224210183192166-312166153222
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ValuationTechnique

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue

ajg:BlackScholesOptionPricingModel



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value9.990.00.00.010.710.00.00.09.270.00.00.011.420.00.00.08.450.00.00.09.250.00.00.09.660.00.00.07.510.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit



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
Value43.710.00.00.039.170.00.09.62000000000000126.090.00.00.023.760.00.00.023.760.00.00.021.280.00.0
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit100.00.00.00.0100.00.00.0100.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

ajg:Range01



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value43.710.00.00.039.170.00.09.62000000000000126.090.00.00.023.760.00.00.023.760.00.00.021.280.00.010.70000000000000110.580.00.00.010.584.790.05.79
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit100.00.00.00.0100.00.00.0100.0100.00.00.00.0100.00.00.00.0100.00.00.00.0100.00.00.00.00.00.00.00.00.00.00.00.0

ajg:Range02



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value46.170.00.00.043.710.00.00.043.710.00.00.043.710.00.00.035.950.04.6100000000000030.031.340.00.00.027.350.00.2400000000000020.079999999999998327.030.00.024.99
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit105.60.00.00.0111.60.00.00.0167.50.00.00.0184.00.00.00.0151.30.00.00.0147.30.00.00.00.00.00.00.00.00.00.00.0

ajg:Range03



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value47.920.00.00.046.170.00.00.046.17-0.69999999999999570.00.046.870.00.00.043.710.00.69999999999999570.046.170.00.04.71000000000000431.240.02.3799999999999990.028.860.00.027.35
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit109.60.00.00.0117.90.00.00.0177.00.00.00.0197.30.00.00.0184.00.00.00.0217.00.00.00.00.00.00.00.00.00.00.00.0

ajg:Range04



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value70.740.00.00.047.920.00.00.047.92-8.9399999999999980.00.056.860.0100000000000051160.00.046.160.01.05000000000000430.046.870.71000000000000090.06.98999999999999539.170.04.7100000000000040.031.240.00.029.45
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit161.80.00.00.0122.30.00.00.0183.70.00.00.0239.30.00.00.0194.30.00.00.0220.30.00.00.00.00.00.00.00.00.00.00.0

ajg:Range05



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-03-31
Value79.590.00.00.070.740.00.00.070.740.046.870.00.00.039.1735.86
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit182.10.00.00.0180.60.00.00.0271.10.00.00.00.00.00.00.0

ajg:Range06



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312014-03-312013-12-312013-09-302013-06-302013-03-312012-09-302012-03-31
Value86.170.00.00.079.5910.580.00.00.010.580.05.79
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit197.10.00.00.0203.20.00.00.00.00.00.00.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit



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
Value86.170.00.00.079.590.00.00.070.746.740000000000002-2.02.056.860.01.62999999999999550.047.920.00.01.050000000000004346.870.00.0
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit100.00.00.00.0100.00.00.00.0100.0100.0100.0100.0100.00.0100.00.0100.00.00.0100.0100.00.00.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

ajg:Range01



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value43.710.00.00.039.170.00.00.039.170.00.00.039.170.00.00.035.710.04.7600000000000020.030.950.00.00.027.250.00.149999999999998580.310000000000002326.790.00.024.9
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit50.70.00.00.049.20.00.00.055.40.0-0.00.068.90.00.00.074.50.00.00.066.00.00.00.00.00.00.00.00.00.00.00.0

ajg:Range02



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value46.870.00.00.043.710.00.00.043.71-2.4600000000000010.00.046.170.00.00.039.170.07.00.039.170.00.04.76000000000000230.950.02.30000000000000070.028.650.00.027.25
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit54.40.00.00.054.90.00.00.061.8-36.5-0.00.081.20.00.00.081.70.00.00.083.60.00.00.00.00.00.00.00.00.00.00.0

ajg:Range03



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value58.860.00.00.046.870.00.00.046.87-9.070.06.39000000000000149.550.00.00.043.710.00.69999999999999570.046.176.9899999999999950.03.21999999999999935.950.04.7600000000000020.030.950.00.029.42
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit68.30.00.00.058.90.00.00.066.3-134.6-0.0319.587.10.00.00.091.20.00.00.098.50.00.00.00.00.00.00.00.00.00.00.0

ajg:Range04



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value70.740.00.00.063.60.00.00.063.66.7400000000000020.00.056.860.01.62999999999999550.047.920.00.01.050000000000004346.870.00.71000000000000096.98999999999999539.170.00.00.035.950.01.960000000000000935.71
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit82.10.00.00.079.90.00.00.089.9100.0-0.00.0100.00.0100.00.0100.00.00.0100.0100.00.00.00.00.00.00.00.00.00.00.00.0

ajg:Range05



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-03-31
Value79.590.00.00.070.740.00.00.070.740.046.870.00.00.039.1735.86
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit92.40.00.00.088.90.00.00.0100.00.00.00.00.00.00.00.0

ajg:Range06



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312014-03-312013-12-312013-09-302013-06-302013-03-312012-09-302012-03-31
Value86.170.00.00.079.5946.870.00.00.039.170.24000000000000235.86
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit100.00.00.00.0100.00.00.00.00.00.00.00.0

us-gaap:StockGrantedDuringPeriodValueSharebasedCompensation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-09-302011-06-302011-03-312010-09-302010-06-30
Value333333314444443333332222212220222122022
Percentage of StockGrantedDuringPeriodValueSharebasedCompensation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value33333314444433333322222122202210
Percentage of StockGrantedDuringPeriodValueSharebasedCompensation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:StockIssuedDuringPeriodSharesAcquisitions

us-gaap:CommonStock



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value700000.0100000.0100000.0500000.00.0500000.0200000.0100000.0
Percentage of StockIssuedDuringPeriodSharesAcquisitions100.0100.0100.0100.00.0100.0100.0100.0

us-gaap:StockIssuedDuringPeriodSharesStockOptionsExercised



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value400000.0400000.0200000.0600000.0700000.0200000.0400000.0100000.0900000.0100000.0200000.0300000.0700000.0200000.0400000.0300000.0200000.00.0200000.0600000.0600000.0200000.0300000.0700000.0500000.0200000.0300000.0800000.01000000.0700000.0400000.01000000.0
Percentage of StockIssuedDuringPeriodSharesStockOptionsExercised100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:CommonStock



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-31
Value0000000000000000000000000001001
Percentage of StockIssuedDuringPeriodSharesStockOptionsExercised100.0100.083.3100.0100.0100.0200.088.9100.0150.0100.085.7100.0100.0100.0100.00.0100.0100.0100.050.0100.085.7120.0100.0100.0100.0100.0100.0100.0110.0

us-gaap:StockIssuedDuringPeriodValueAcquisitions



Period End2020-03-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312012-09-302012-03-312011-03-31
Value7391137371461715141352044205851956011388633381149161048627
Percentage of StockIssuedDuringPeriodValueAcquisitions100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302012-12-312012-09-302012-03-312011-03-31
Value72810363371461714141352043204841915911086623379146161018426
Percentage of StockIssuedDuringPeriodValueAcquisitions99.098.999.198.60.098.798.698.598.398.798.697.898.398.197.797.696.097.997.997.897.997.797.897.997.897.797.097.297.296.7

us-gaap:CommonStock



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-12-312012-09-302012-03-312011-03-31
Value00000000000000100141221010220
Percentage of StockIssuedDuringPeriodValueAcquisitions1.01.10.91.40.01.31.41.51.71.31.42.21.71.92.32.44.02.12.12.22.12.32.22.12.23.02.82.83.3

us-gaap:StockIssuedDuringPeriodValueEmployeeStockPurchasePlan



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value661044594474336422532243224211211
Percentage of StockIssuedDuringPeriodValueEmployeeStockPurchasePlan100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value561044584474336322532243223211111
Percentage of StockIssuedDuringPeriodValueEmployeeStockPurchasePlan98.398.499.097.998.098.198.997.697.698.697.896.996.998.497.596.2100.096.4100.095.796.097.9100.095.295.597.5100.094.494.495.093.392.9

us-gaap:CommonStock



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value100000.0100000.0100000.0100000.0100000.0100000.0100000.0100000.0100000.0100000.0100000.0100000.0100000.0100000.0100000.0100000.00.0200000.00.0100000.0100000.0100000.00.0100000.0100000.0100000.00.0100000.0100000.0100000.0100000.0100000.0
Percentage of StockIssuedDuringPeriodValueEmployeeStockPurchasePlan1.71.61.02.12.01.91.12.42.41.42.23.13.11.62.53.80.03.60.04.34.02.10.04.84.52.50.05.65.65.06.77.1

us-gaap:StockIssuedDuringPeriodValueStockOptionsExercised



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value171121287166286810175910415171547151659222519102524
Percentage of StockIssuedDuringPeriodValueStockOptionsExercised100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:AdditionalPaidInCapital



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value171121276166275791659941517154714155821241892424
Percentage of StockIssuedDuringPeriodValueStockOptionsExercised97.898.397.797.597.297.696.997.298.396.297.096.596.495.997.095.2100.096.296.696.298.096.296.196.296.296.796.496.096.496.195.696.4

us-gaap:CommonStock



Period End2020-03-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-03-31
Value00000000000000000000000000010010
Percentage of StockIssuedDuringPeriodValueStockOptionsExercised2.21.72.32.52.82.43.12.81.73.83.03.53.64.13.04.80.03.83.43.82.03.83.93.83.83.33.64.03.63.94.43.6

ajg:AccruedCompensationAndOtherAccruedLiabilities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value10581347125510679991055864768711818772651658728812648633654623560491471370361284343306285244214304246216165226190188214
Percentage of AccruedCompensationAndOtherAccruedLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:AccruedSupplementalDirectBillAndOtherReceivablesCurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-31
Value31736938336830634830225122915417218117017714516614518116719313015669
Percentage of AccruedSupplementalDirectBillAndOtherReceivablesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:BusinessAcquisitionCostOfAcquiredEntityPurchasePriceNet



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value34717911272953267101471850688545417305196399264174656274943078822892078152643103649198
Percentage of BusinessAcquisitionCostOfAcquiredEntityPurchasePriceNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FiniteLivedIntangibleAssetsByMajorClass, us-gaap:StatementBusinessSegments

ajg:BusinessAcquisitionPurchasePriceAllocationGoodwillNotExpectedTaxDeductibleAmount

ajg:ExpirationLists, ajg:BrokerageSegment



Period End2020-03-31
Value1
Percentage of BusinessAcquisitionPurchasePriceAllocationGoodwillNotExpectedTaxDeductibleAmount100.0

us-gaap:NoncompeteAgreements, ajg:BrokerageSegment



Period End2020-03-31
Value0.0
Percentage of BusinessAcquisitionPurchasePriceAllocationGoodwillNotExpectedTaxDeductibleAmount0.0

us-gaap:TradeNames, ajg:BrokerageSegment



Period End2020-03-31
Value0.0
Percentage of BusinessAcquisitionPurchasePriceAllocationGoodwillNotExpectedTaxDeductibleAmount0.0

ajg:BusinessAcquisitionsPurchasePriceAllocationGoodwillAmount



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value1599757566041315844042944130422815491225147893335424514343144812238782066530049
Percentage of BusinessAcquisitionsPurchasePriceAllocationGoodwillAmount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAccruedLiability



Period End2020-03-31
Value1
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAccruedLiability100.0

us-gaap:BusinessAcquisition

ajg:OtherAcquisition



Period End2020-03-31
Value1
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAccruedLiability100.0

ajg:EquityMethodInvestmentSummarizedFinancialInformationFundingCommitments



Period End2020-03-312019-09-302018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value130000000031219105828223411101916715211162
Percentage of EquityMethodInvestmentSummarizedFinancialInformationFundingCommitments100.0100.00.00.00.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ScheduleOfEquityMethodInvestmentEquityMethodInvesteeName, us-gaap:InvestmentType, us-gaap:StatementEquityComponents

ajg:CleanCoalInvestments, ajg:NineteenTwoThousandElevenEraCleanCoalProductionPlants, ajg:ControllingInterest



Period End2020-03-31
Value1
Percentage of EquityMethodInvestmentSummarizedFinancialInformationFundingCommitments100.0

ajg:ExpirationLists



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value159841527374130381318204462411881481052181319334263233150408957905751839420854733522513057160130120
Percentage of ExpirationLists100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:MaximumPotentialEarnoutPayable



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value2424772882118120112071312011461106810753425202162149331981325921119472162351568641956847
Percentage of MaximumPotentialEarnoutPayable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:LineOfCreditFacility, us-gaap:ShortTermDebtType

ajg:NumberOfLetterOfCreditIssued

ajg:RentCaptiveFacility, us-gaap:LetterOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value7.07.07.07.07.07.07.07.07.00.00.07.0
Percentage of NumberOfLetterOfCreditIssued100.0100.0100.0100.0100.0100.0100.0100.0100.00.00.0100.0

ajg:SelfInsuranceDeductibles, us-gaap:LetterOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312017-03-31
Value2.02.02.02.02.02.02.02.00.00.02.02.0
Percentage of NumberOfLetterOfCreditIssued28.628.628.628.628.628.628.628.60.00.028.6

us-gaap:ShortTermDebtType

us-gaap:LetterOfCredit



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-30
Value1.01.01.01.01.01.01.01.00.00.01.00.00.00.01.00.00.00.01.00.00.0
Percentage of NumberOfLetterOfCreditIssued14.314.314.314.30.014.314.314.30.00.014.30.00.00.00.00.00.00.00.00.00.0

ajg:PremiumFinancingBorrowings



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-31
Value122170170137134154159111121151156100104125133101961371149195127
Percentage of PremiumFinancingBorrowings100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:PremiumsPayableToUnderwritingEnterprises



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312016-12-31
Value77786348657368736741574056935982607134752996
Percentage of PremiumsPayableToUnderwritingEnterprises100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AwardType

ajg:ProvisionalCompensationCashAwardApprovedForFutureGrantByCompensationCommitteeUnits

ajg:TwoThousandSeventeenProvisionalCashAwards



Period End2020-03-312017-12-31
Value221600.0242000.0
Percentage of ProvisionalCompensationCashAwardApprovedForFutureGrantByCompensationCommitteeUnits100.0100.0

us-gaap:TitleOfIndividual, us-gaap:AwardType

srt:Officer, ajg:CashAwards



Period End2020-03-312020-03-122019-12-312019-09-302019-03-312019-03-142018-03-312018-03-152017-03-16
Value02130000000000
Percentage of ProvisionalCompensationCashAwardApprovedForFutureGrantByCompensationCommitteeUnits90.30.00.00.00.00.00.00.00.0

us-gaap:TitleOfIndividual, us-gaap:AwardType

ajg:ProvisionalCompensationCashAwardApprovedForFutureGrantByCompensationCommitteeValue

srt:Officer, ajg:CashAwards



Period End2020-03-122019-03-142018-03-152017-03-16
Value18161514
Percentage of ProvisionalCompensationCashAwardApprovedForFutureGrantByCompensationCommitteeValue100.0100.0100.0100.0

ajg:RefinedCoalProductionRelatedReceivablesCurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-31
Value47103131117114160158173128156125147121136122133801081351309210356
Percentage of RefinedCoalProductionRelatedReceivablesCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:SemiAnnualPaymentsOfInterest



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value490046134483438541923617353734943279313930293118294928532791273625262457239223712335239224212517189214551060925775854725767685675710550
Percentage of SemiAnnualPaymentsOfInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:SemiAnnualPaymentsOfInterestNet



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312015-12-31
Value489246064475437741853610353034873273313330233112294428482453
Percentage of SemiAnnualPaymentsOfInterestNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AwardType

ajg:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionNonvestedIntrinsicValue

ajg:UnvestedRestrictedStock



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value153215201199142140141125121109
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionNonvestedIntrinsicValue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AccountsReceivableBilledForLongTermContractsOrPrograms



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-312012-12-312011-12-31
Value271388362340305316331302246305292257220241255230197220217219194232222
Percentage of AccountsReceivableBilledForLongTermContractsOrPrograms100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:AdditionalPaidInCapitalCommonStock



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value3909382536973656360635413516344634053388336633233280326532393191320232093193309127222649249423881405135812591092108610551017899803693638615563507439417349
Percentage of AdditionalPaidInCapitalCommonStock100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique

us-gaap:AlternativeInvestmentMeasurementInput

ajg:TwoThousandTwentyAcquisitions, us-gaap:MeasurementInputDiscountRate, us-gaap:IncomeApproachValuationTechnique



Period End2020-03-31
Value9.0
Percentage of AlternativeInvestmentMeasurementInput100.0

us-gaap:Range, us-gaap:BusinessAcquisition, us-gaap:MeasurementInputType, us-gaap:ValuationTechnique

srt:Maximum, ajg:TwoThousandEighteenAcquisitions, us-gaap:MeasurementInputLongTermRevenueGrowthRate, us-gaap:MarketApproachValuationTechnique



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value3.23.03.03.03.215.015.015.0
Percentage of AlternativeInvestmentMeasurementInput35.60.00.00.00.00.00.00.0

srt:Maximum, ajg:TwoThousandTwentyAcquisitions, us-gaap:MeasurementInputDiscountRate, us-gaap:MarketApproachValuationTechnique



Period End2020-03-31
Value13.8
Percentage of AlternativeInvestmentMeasurementInput153.3

srt:Minimum, ajg:TwoThousandEighteenAcquisitions, us-gaap:MeasurementInputLongTermRevenueGrowthRate, us-gaap:IncomeApproachValuationTechnique



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-31
Value10.010.010.512.010.010.0
Percentage of AlternativeInvestmentMeasurementInput111.10.00.00.00.00.0

srt:Minimum, ajg:TwoThousandEighteenAcquisitions, us-gaap:MeasurementInputLongTermRevenueGrowthRate, us-gaap:MarketApproachValuationTechnique



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-30
Value3.02.02.02.53.03.03.03.0
Percentage of AlternativeInvestmentMeasurementInput33.30.00.00.00.00.00.00.0

srt:Minimum, ajg:TwoThousandTwentyAcquisitions, us-gaap:MeasurementInputDiscountRate, us-gaap:MarketApproachValuationTechnique



Period End2020-03-31
Value2.5
Percentage of AlternativeInvestmentMeasurementInput27.8

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value37320941519113731512939226209760246633221253235721480774596339110345431002408441393637145
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value24525183191312096421310834332686753050162
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:HanoverExcessAndSurplusIncAndHanoverPremiumFinanceInc



Period End2020-03-31
Value300000.0
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents11.5

ajg:OtherAcquisition



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value21132111650
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents88.525.713.910.927.060.246.740.750.0

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value241671449540206131597383619116762187138103331997595385902619933
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:HanoverExcessAndSurplusIncAndHanoverPremiumFinanceInc



Period End2020-03-31
Value4
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther16.5

ajg:OtherAcquisition



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value206960161410343204
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther83.541.741.717.236.050.032.734.753.3

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value22217191143431771155363734191067612110127912518771746650030211736
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:HanoverExcessAndSurplusIncAndHanoverPremiumFinanceInc



Period End2020-03-31
Value4
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities19.5

ajg:OtherAcquisition



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value18615014129443193
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities80.528.426.69.828.353.237.636.157.1

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value2630324718448278203113956492615132934014146102322111651022882135714647
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:HanoverExcessAndSurplusIncAndHanoverPremiumFinanceInc



Period End2020-03-31
Value4
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities18.8

ajg:OtherAcquisition



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value218769211314567345
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities81.228.828.211.728.152.132.930.257.6

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value347179112729532671014718506885454173051963992641746562749430788228920781526431036491981361440023489406334295
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value10383521526980000111010001514114320
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.00.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:CapsicumReinsuranceBrokersLLP



Period End2020-03-31
Value7
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets74.5

ajg:HanoverExcessAndSurplusIncAndHanoverPremiumFinanceInc



Period End2020-03-31
Value800000.0
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets7.8

ajg:OtherAcquisition



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-30
Value1131242170
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets17.635.236.221.038.266.82.2

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-30
Value38555401008860219147565321831910733942752320552811
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:HanoverExcessAndSurplusIncAndHanoverPremiumFinanceInc



Period End2020-03-31
Value500000.0
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities14.7

ajg:OtherAcquisition



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302018-03-31
Value2251875023151
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities85.329.833.518.550.026.725.058.6

us-gaap:BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302013-12-312013-09-302013-06-30
Value010751864243113310876-32928201062
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:OtherAcquisition



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value032001000
Percentage of BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment100.031.431.99.626.318.110.88.314.3

us-gaap:CapitalizedContractCostAccumulatedAmortization



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-31
Value12035527719111330924016810028322015391
Percentage of CapitalizedContractCostAccumulatedAmortization100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:CapitalizedContractCostNet



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value57986464559158554883
Percentage of CapitalizedContractCostNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ContractWithCustomerLiability



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-312016-12-31
Value491503493504480457430404
Percentage of ContractWithCustomerLiability100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-312016-12-31
Value332337327333309284258233
Percentage of ContractWithCustomerLiability67.766.966.266.264.562.260.157.8

ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312017-12-312016-12-31
Value159166166170170173171170
Percentage of ContractWithCustomerLiability32.333.133.833.835.537.839.942.2

us-gaap:LineOfCreditFacility, us-gaap:LongtermDebtType, us-gaap:SubsequentEventType, us-gaap:SubsidiarySaleOfStock

us-gaap:DebtWeightedAverageInterestRate

ajg:NotePurchaseAgreement, ajg:UnsecuredNotes, us-gaap:SubsequentEvent, us-gaap:PrivatePlacement



Period End2020-01-30
Value0.0423
Percentage of DebtWeightedAverageInterestRate100.0

us-gaap:DeferredRevenue



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value491503493504480457472471465430
Percentage of DeferredRevenue100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredRevenueCurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value423434421429402379396395390355
Percentage of DeferredRevenueCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredRevenueNoncurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value68697275787876767475
Percentage of DeferredRevenueNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DeferredTaxAssetsNetNoncurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value1003945952905869806743716708905918861806796749702660521487438395392352328292279283275258251240237236240214234242245244255271
Percentage of DeferredTaxAssetsNetNoncurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeAssetNotionalAmount



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-31
Value52173591371510761713
Percentage of DerivativeAssetNotionalAmount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BalanceSheetLocation, us-gaap:DerivativeInstrumentRisk

us-gaap:OtherCurrentAssets, us-gaap:ForeignExchangeContract



Period End2020-03-312019-12-312019-09-302019-06-302018-12-31
Value14100
Percentage of DerivativeAssetNotionalAmount28.021.221.626.59.4

us-gaap:OtherNoncurrentAssets, us-gaap:ForeignExchangeContract



Period End2020-03-312019-12-31
Value38
Percentage of DerivativeAssetNotionalAmount72.040.1

us-gaap:DerivativeInstrumentRisk, us-gaap:FinancialInstrument

us-gaap:DerivativeInstrumentsAndHedges

us-gaap:ForeignExchangeContract, us-gaap:ForwardContracts



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312015-12-31
Value131222272623192726135437466143
Percentage of DerivativeInstrumentsAndHedges100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:DerivativeInstrumentRisk, us-gaap:FinancialInstrument, us-gaap:OptionIndexedToIssuersEquityType

us-gaap:ForeignExchangeContract, us-gaap:ForwardContracts, us-gaap:CallOption



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302017-12-312017-09-302017-06-302017-03-312016-12-312015-12-31
Value35435163687280314144535757
Percentage of DerivativeInstrumentsAndHedges270.2362.0233.8232.4253.2315.6418.2233.174.7118.4113.293.3131.0

us-gaap:DerivativeInstrumentRisk, us-gaap:OptionIndexedToIssuersEquityType

us-gaap:ForeignExchangeContract, us-gaap:CallOption



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-31
Value30334230421524827610596128141135869578
Percentage of DerivativeInstrumentsAndHedges2316.02826.41373.4790.4924.91196.5549.0354.0480.51060.2247.4229.9203.6127.1

us-gaap:ForeignExchangeContract, us-gaap:PutOption



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-31
Value30334230421524827610592128141134869578
Percentage of DerivativeInstrumentsAndHedges2316.02826.41373.4790.4924.91196.5549.0338.2480.51060.2244.4229.9203.6127.1

us-gaap:DerivativeLiabilityNotionalAmount



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312015-12-31
Value1565293563625962210712171
Percentage of DerivativeLiabilityNotionalAmount100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BalanceSheetLocation, us-gaap:DerivativeInstrumentRisk

ajg:AccruedCompensationAndOtherCurrentLiabilities, us-gaap:ForeignExchangeContract



Period End2020-03-312019-12-312019-09-302019-06-302018-12-31
Value61734
Percentage of DerivativeLiabilityNotionalAmount4.33.47.55.819.0

ajg:AccruedCompensationAndOtherCurrentLiabilities, us-gaap:InterestRateContract



Period End2020-03-312019-12-312019-09-302019-06-302018-12-31
Value6325432013
Percentage of DerivativeLiabilityNotionalAmount40.847.746.835.950.4

us-gaap:OtherNoncurrentLiabilities, us-gaap:ForeignExchangeContract



Period End2020-03-312019-12-31
Value82
Percentage of DerivativeLiabilityNotionalAmount5.25.0

us-gaap:OtherNoncurrentLiabilities, us-gaap:InterestRateContract



Period End2020-03-312019-12-312019-09-302019-06-30
Value77233328
Percentage of DerivativeLiabilityNotionalAmount49.743.935.551.2

us-gaap:DerivativeNotionalAmount



Period End2020-03-312019-12-312019-09-302018-12-31
Value922831929901
Percentage of DerivativeNotionalAmount100.0100.0100.0100.0

us-gaap:DerivativeInstrumentRisk

us-gaap:ForeignExchangeContract



Period End2020-03-312019-12-312019-09-302018-12-31
Value22312951
Percentage of DerivativeNotionalAmount2.43.83.25.7

us-gaap:InterestRateContract



Period End2020-03-312019-12-312019-09-302018-12-31
Value900800900850
Percentage of DerivativeNotionalAmount97.696.296.894.3

us-gaap:EquityMethodInvestmentSummarizedFinancialInformationAssets



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value334041495459656974798489939389858483818380829096102908765565445424456342222
Percentage of EquityMethodInvestmentSummarizedFinancialInformationAssets100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ScheduleOfEquityMethodInvestmentEquityMethodInvesteeName

ajg:VentureCapitalFundsAndOther



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302010-12-31
Value4444454443333322222233333333233322222
Percentage of EquityMethodInvestmentSummarizedFinancialInformationAssets13.211.210.78.98.98.47.56.75.64.84.44.24.13.92.93.13.23.13.23.04.13.93.53.33.04.14.15.35.25.57.37.84.53.56.710.38.8

us-gaap:ScheduleOfEquityMethodInvestmentEquityMethodInvesteeName, us-gaap:InvestmentType, us-gaap:StatementEquityComponents

ajg:CleanCoalInvestments, ajg:NineteenTwoThousandElevenEraCleanCoalProductionPlants, ajg:ControllingInterest



Period End2020-03-312019-12-31
Value2229
Percentage of EquityMethodInvestmentSummarizedFinancialInformationAssets68.373.0

ajg:CleanCoalInvestments, ajg:OneTwoThousandElevenEraCleanCoalProductionPlants, us-gaap:NoncontrollingInterest



Period End2020-03-312019-12-31
Value200000.0300000.0
Percentage of EquityMethodInvestmentSummarizedFinancialInformationAssets0.60.8

us-gaap:EscrowDeposit



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value772523019715435834251812221412334271634232252392500191442885
Percentage of EscrowDeposit100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:FiniteLivedIntangibleAssetsAccumulatedAmortization

ajg:ExpirationLists



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302010-12-31
Value2076200418901824175816761614154714981422136512781210114310971039987934870823764719675631548511477444417390367341317296272225
Percentage of FiniteLivedIntangibleAssetsAccumulatedAmortization100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:NoncompeteAgreements



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302010-12-31
Value525252514948484747464544434240393634333230292827262525242323222221212019
Percentage of FiniteLivedIntangibleAssetsAccumulatedAmortization2.52.62.82.82.82.93.03.13.23.23.33.53.63.73.73.83.73.73.83.94.04.14.24.34.85.15.25.55.76.06.26.56.97.27.68.7

us-gaap:TradeNames



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302010-12-31
Value3030292726252323232222201918171615141312101098766555443322
Percentage of FiniteLivedIntangibleAssetsAccumulatedAmortization1.51.51.51.51.51.51.51.51.61.61.61.61.61.61.61.61.61.51.51.51.41.41.41.31.31.31.41.31.31.31.31.21.21.11.11.0

us-gaap:FiniteLivedIntangibleAssetsByMajorClass

us-gaap:FiniteLivedIntangibleAssetsGross

ajg:ExpirationLists



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302010-12-31
Value4231424638803749352933793342323331283055302529282880275727132681263926132590256024582461240922321620156313721207116511751066965895837808699
Percentage of FiniteLivedIntangibleAssetsGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:NoncompeteAgreements



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302010-12-31
Value706876746058555454535352504948494843424243434437333731303030302826262523
Percentage of FiniteLivedIntangibleAssetsGross1.71.62.02.01.71.71.71.71.71.81.81.81.81.81.81.81.81.71.61.71.81.81.81.72.02.42.32.52.62.62.82.93.03.13.13.4

us-gaap:TradeNames



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302010-12-31
Value104918988868660602625262424242424252526272829312822222221202320191919198
Percentage of FiniteLivedIntangibleAssetsGross2.52.22.32.42.42.51.81.90.80.80.90.80.80.90.90.91.01.01.01.11.21.21.31.31.41.41.61.81.72.01.92.02.22.32.41.2

us-gaap:FiniteLivedNoncompeteAgreementsGross



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-30
Value41121162521032212121321011125171105421212
Percentage of FiniteLivedNoncompeteAgreementsGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:FiniteLivedTradeNamesGross



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302017-12-312016-12-312016-09-302015-12-312014-12-312014-09-302014-06-302013-12-312013-09-302013-06-302012-12-312012-09-302011-12-312011-09-30
Value1342261353500009105111301111
Percentage of FiniteLivedTradeNamesGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:BusinessAcquisition

ajg:BusinessAcquisition



Period End2020-03-31
Value13
Percentage of FiniteLivedTradeNamesGross100.0

ajg:CapsicumReinsuranceBrokersLLP



Period End2020-03-31
Value13
Percentage of FiniteLivedTradeNamesGross100.0

us-gaap:StatementBusinessSegments

ajg:InsuranceBrokerageAndRiskManagementServices



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-302017-12-312016-12-312016-09-302015-12-31
Value134226135350000
Percentage of FiniteLivedTradeNamesGross100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:OperatingLeaseLiabilityNoncurrent



Period End2020-03-312019-12-312019-09-302019-06-30
Value319340335327
Percentage of OperatingLeaseLiabilityNoncurrent100.0100.0100.0100.0

us-gaap:PremiumsAndOtherReceivablesNet



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-312011-12-312011-09-302011-06-302011-03-312010-12-312010-09-302010-06-302009-12-31
Value70945419568460076253485748725142567521572227237420661844168320381706173416001764154314621669199712531288107512451050109610311367108010279821292718750704916693
Percentage of PremiumsAndOtherReceivablesNet100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PrepaidExpenseCurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-31
Value10611595101951089995959189788178777480797180687248
Percentage of PrepaidExpenseCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:Range, us-gaap:LineOfCreditFacility

us-gaap:ProductLiabilityContingencyAccrualPresentValue

srt:Maximum, ajg:ErrorsAndOmissions



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-30
Value3488777
Percentage of ProductLiabilityContingencyAccrualPresentValue100.0100.0100.0100.0100.0100.0100.0

srt:Minimum, ajg:ErrorsAndOmissions



Period End2020-03-312019-12-312019-09-302019-06-302018-12-312018-09-302018-06-30
Value3201011
Percentage of ProductLiabilityContingencyAccrualPresentValue112.957.19.313.38.914.722.5

us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

us-gaap:RecordedUnconditionalPurchaseObligation

ajg:ContractualObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value707565986501642561585222526654184742461245954497423441694786433740173944365338183623366938503805284821081692155413441375
Percentage of RecordedUnconditionalPurchaseObligation100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:DebtObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value64935978587658195552469546594642417340593983392636603593352634993170312930873094308131663227334324551712132512069941090
Percentage of RecordedUnconditionalPurchaseObligation91.890.690.490.690.289.988.585.788.088.086.787.386.586.273.780.778.979.384.581.085.086.383.887.986.281.278.377.674.079.3

ajg:InterestOnDebt



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value15931364139314331359107811221148894920954808711740735762644672694722745
Percentage of RecordedUnconditionalPurchaseObligation22.520.721.422.322.120.721.321.218.920.020.818.016.817.815.417.616.017.119.018.920.6

ajg:NotePurchaseAgreement



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value4498392339233923379831983248324827982798279827002450245024002400212521252125212521252125212522251525925925925725725725675675
Percentage of RecordedUnconditionalPurchaseObligation63.659.560.361.161.761.261.759.959.060.760.960.057.958.850.155.352.953.958.255.758.657.955.258.553.543.954.759.553.952.70.00.00.0

ajg:OperatingLeaseObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value4504794734514564704825154944804864764734681100659695683503508510469592422352350350325322251255249255
Percentage of RecordedUnconditionalPurchaseObligation6.47.37.37.07.49.09.29.510.410.410.610.611.211.223.015.217.317.313.813.314.112.815.411.112.416.620.720.924.018.30.00.00.0

ajg:OutstandingPurchaseObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value1321431551581536015014279748495101108161179151133647037363543444822263138222521
Percentage of RecordedUnconditionalPurchaseObligation1.92.22.42.52.51.22.92.61.71.61.82.12.42.63.44.13.83.41.81.81.01.00.91.11.62.31.31.72.32.80.00.00.0

ajg:PremiumFinancingDebtFacility



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value122170170137134154159111121151156100104125133101961371149195
Percentage of RecordedUnconditionalPurchaseObligation1.72.62.62.12.22.93.02.12.63.33.42.22.53.02.82.32.43.53.12.42.6

ajg:UnsecuredMulticurrencyCreditAgreement



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-03-312012-12-312012-06-302012-03-31
Value28052039032526026513013536019075318395278258235305195153155115140147153367530135501294892
Percentage of RecordedUnconditionalPurchaseObligation4.07.96.05.14.25.12.52.57.64.11.67.19.36.75.45.47.64.94.24.13.23.83.84.012.925.28.03.79.40.00.0

us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

us-gaap:RecordedUnconditionalPurchaseObligationDueAfterFifthYear

ajg:ContractualObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value4195344840354019375629533428345327092695303325122177216826322349199519832081207920602030231421981367566660649407349
Percentage of RecordedUnconditionalPurchaseObligationDueAfterFifthYear100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:DebtObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value4093334738973896363928673280328025912591289123832055205520902090173017301898189818981898207220721276479551551318318
Percentage of RecordedUnconditionalPurchaseObligationDueAfterFifthYear97.697.196.697.096.997.195.795.095.696.195.394.994.494.879.489.086.787.291.291.392.293.589.594.393.384.783.584.978.291.0

ajg:InterestOnDebt



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value745574699698616444557557368368468358280280340340255255323323323
Percentage of RecordedUnconditionalPurchaseObligationDueAfterFifthYear17.816.717.317.416.415.016.316.113.613.715.514.312.912.912.914.512.812.915.615.615.7

ajg:NotePurchaseAgreement



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value3348277331983198302324232723272322232223242320251775177517501750147514751575157515751575167516751025425475475275275575525525
Percentage of RecordedUnconditionalPurchaseObligationDueAfterFifthYear79.880.479.379.680.582.079.478.982.182.579.980.681.581.966.574.573.974.475.775.776.477.672.476.274.975.071.973.167.678.60.00.00.0

ajg:OperatingLeaseObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value858411510094871321441191041411291211125422542652531761731611312421269186109978831534544
Percentage of RecordedUnconditionalPurchaseObligationDueAfterFifthYear2.02.42.92.52.53.03.94.24.43.94.75.15.65.220.610.813.312.88.58.37.86.510.55.76.715.316.515.121.89.00.00.00.0

ajg:OutstandingPurchaseObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302016-06-302015-09-302015-06-302012-09-302012-06-302012-03-31
Value17172323232828467000
Percentage of RecordedUnconditionalPurchaseObligationDueAfterFifthYear0.40.50.60.60.60.80.80.20.30.30.00.00.0

us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

us-gaap:RecordedUnconditionalPurchaseObligationDueInFifthYear

ajg:ContractualObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value682660518509498457388390354349241220206202298256244235233228218212232218131100381377367357
Percentage of RecordedUnconditionalPurchaseObligationDueInFifthYear100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:DebtObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value63360945045044241332232230030018016415415418018016816817317317317317717710071341341333333
Percentage of RecordedUnconditionalPurchaseObligationDueInFifthYear92.792.386.988.488.890.483.182.684.786.074.874.774.676.560.770.568.971.674.275.879.381.776.281.476.171.589.490.390.893.4

ajg:InterestOnDebt



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value15813415015014211312212210010010589797980806868737373
Percentage of RecordedUnconditionalPurchaseObligationDueInFifthYear23.120.429.129.528.624.731.631.428.328.843.840.738.439.427.131.528.029.131.432.033.5

ajg:NotePurchaseAgreement



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value475475300300300300200200200200757575751001001001001001001001001001005050300300300300505050
Percentage of RecordedUnconditionalPurchaseObligationDueInFifthYear69.671.957.958.960.165.651.551.356.457.231.134.036.237.133.639.040.842.542.843.745.847.242.945.938.049.878.679.481.683.90.00.00.0

ajg:OperatingLeaseObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value4445595148445757524758535045109676763534945385540312840363323302624
Percentage of RecordedUnconditionalPurchaseObligationDueInFifthYear6.56.811.410.19.79.714.814.714.913.524.324.324.322.736.626.227.726.923.021.420.918.323.718.523.728.210.59.69.16.50.00.00.0

ajg:OutstandingPurchaseObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value55887101022222188836600000000111
Percentage of RecordedUnconditionalPurchaseObligationDueInFifthYear0.80.91.71.61.62.82.80.60.60.91.01.10.82.73.33.41.52.83.00.20.10.20.30.10.10.10.10.00.00.0

us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

us-gaap:RecordedUnconditionalPurchaseObligationDueInFourthYear

ajg:ContractualObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value547525453443428385293289250245288266252248323279260250250245234227470455415384145138128120
Percentage of RecordedUnconditionalPurchaseObligationDueInFourthYear100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:DebtObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value47545236036035232220220218118021019418418418518517317317717717717739739736934194948686
Percentage of RecordedUnconditionalPurchaseObligationDueInFourthYear86.986.279.581.382.483.769.170.072.173.873.073.073.174.257.466.366.469.170.872.475.678.084.487.388.988.864.568.067.772.0

ajg:InterestOnDebt



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value17515216016015212212712710610511094848485857373777777
Percentage of RecordedUnconditionalPurchaseObligationDueInFourthYear32.129.035.336.135.631.843.544.142.243.138.335.533.434.026.430.528.129.230.931.633.0

ajg:NotePurchaseAgreement



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value3003002002002002007575757510010010010010010010010010010010010030030030030050505050
Percentage of RecordedUnconditionalPurchaseObligationDueInFourthYear54.857.144.145.146.751.925.625.929.930.634.637.539.740.330.935.738.339.939.940.842.644.063.765.972.278.134.336.239.041.5

ajg:OperatingLeaseObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value6263746661617473686270646056121787873666157497257454250434032403634
Percentage of RecordedUnconditionalPurchaseObligationDueInFourthYear11.512.216.515.014.415.925.325.327.225.524.424.324.122.737.427.930.229.426.524.924.521.915.512.510.910.934.731.131.326.90.00.00.0

ajg:OutstandingPurchaseObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value9918161421914227777171694670010001111111
Percentage of RecordedUnconditionalPurchaseObligationDueInFourthYear1.61.74.13.83.30.56.54.90.90.92.72.82.93.15.35.83.41.62.73.00.20.10.20.20.20.20.90.91.01.10.00.00.0

us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

us-gaap:RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear

ajg:ContractualObligations



Period End2020-03-312019-09-302019-06-302019-03-31
Value758705682740
Percentage of RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear100.0100.0100.0100.0

ajg:DebtObligation



Period End2020-03-312019-09-302019-06-302019-03-31
Value640656599620
Percentage of RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear84.593.187.983.8

ajg:InterestOnDebt



Period End2020-03-312019-09-302019-06-302019-03-31
Value1384687126
Percentage of RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear18.26.612.817.0

ajg:NotePurchaseAgreement



Period End2020-03-312019-09-302019-06-302019-03-31
Value1005050100
Percentage of RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear13.27.17.313.5

ajg:OperatingLeaseObligation



Period End2020-03-312019-09-302019-06-302019-03-31
Value77214879
Percentage of RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear10.23.17.110.8

ajg:OutstandingPurchaseObligations



Period End2020-03-312019-09-302019-06-302019-03-31
Value40263441
Percentage of RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear5.43.85.15.5

ajg:PremiumFinancingDebtFacility



Period End2020-03-312019-09-302019-06-302019-03-31
Value122170137134
Percentage of RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear16.224.120.118.2

ajg:UnsecuredMulticurrencyCreditAgreement



Period End2020-03-312019-09-302019-06-302019-03-31
Value280390325260
Percentage of RecordedUnconditionalPurchaseObligationDueInRemainderOfFiscalYear36.955.347.735.1

us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

us-gaap:RecordedUnconditionalPurchaseObligationDueInSecondYear

ajg:ContractualObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value404380417412393338380374333322356332313308606561529513260255245236224199156124227220209204
Percentage of RecordedUnconditionalPurchaseObligationDueInSecondYear100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:DebtObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value2652422702712632322372372152152192031921934094093973971501501501501001007244150150143143
Percentage of RecordedUnconditionalPurchaseObligationDueInSecondYear65.763.764.865.766.968.762.363.464.566.761.661.361.562.667.573.075.177.457.758.861.363.544.750.346.135.566.168.368.169.8

ajg:InterestOnDebt



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value19016717017116313213713711511511910392931091099797100100100
Percentage of RecordedUnconditionalPurchaseObligationDueInSecondYear47.244.040.941.541.539.136.136.734.535.733.631.229.630.218.119.618.419.038.539.240.9

ajg:NotePurchaseAgreement



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-09-302013-06-302013-03-312012-12-31
Value757510010010010010010010010010010010010030030030030050505050100100100100
Percentage of RecordedUnconditionalPurchaseObligationDueInSecondYear18.519.723.924.325.429.526.326.730.031.028.030.131.932.449.453.556.758.419.219.520.421.144.045.447.648.8

ajg:OperatingLeaseObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value101100107100939210310094881019488831541101091039592908110483696569605751645956
Percentage of RecordedUnconditionalPurchaseObligationDueInSecondYear25.226.425.824.323.627.227.126.728.427.428.428.528.327.125.419.820.720.136.736.036.734.546.541.844.452.830.527.627.525.10.00.00.0

ajg:OutstandingPurchaseObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value373840413714433824193534323243402213151465211615159101012995
Percentage of RecordedUnconditionalPurchaseObligationDueInSecondYear9.210.09.610.19.64.311.410.17.36.010.110.410.310.47.27.34.32.65.95.72.62.39.48.410.112.44.14.85.15.90.00.00.0

us-gaap:RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchased

us-gaap:RecordedUnconditionalPurchaseObligationDueInThirdYear

ajg:ContractualObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value4874653713593412923493443032923192962792733573142872724924864744662412291881561121039386
Percentage of RecordedUnconditionalPurchaseObligationDueInThirdYear100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

ajg:DebtObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-31
Value3853612402402322022322322102102151991881891891891771773973973973971501501229444443636
Percentage of RecordedUnconditionalPurchaseObligationDueInThirdYear79.077.864.867.068.369.466.667.669.471.967.267.167.669.053.060.461.765.280.781.783.885.262.365.664.960.139.342.839.542.5

ajg:InterestOnDebt



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-31
Value18516116516515712713213211011011599888989897777979797
Percentage of RecordedUnconditionalPurchaseObligationDueInThirdYear38.034.844.646.146.343.738.038.636.537.836.033.431.832.525.128.626.928.519.820.020.6

ajg:NotePurchaseAgreement



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312012-09-302012-06-302012-03-31
Value2002007575757510010010010010010010010010010010010030030030030050505050100100100
Percentage of RecordedUnconditionalPurchaseObligationDueInThirdYear41.043.020.220.922.025.628.629.133.034.131.333.735.836.527.931.834.836.760.961.763.264.320.721.826.631.90.00.00.0

ajg:OperatingLeaseObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value7980948579788785807485797368136939286858076688869565361525043484341
Percentage of RecordedUnconditionalPurchaseObligationDueInThirdYear16.417.325.323.723.326.925.124.926.425.426.826.626.225.038.129.632.331.917.416.516.214.736.730.530.234.155.151.153.850.10.00.00.0

ajg:OutstandingPurchaseObligations



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value2223373429113126138191817163131178991039997767554
Percentage of RecordedUnconditionalPurchaseObligationDueInThirdYear4.75.010.19.58.63.99.17.74.42.86.06.36.26.18.99.96.03.02.01.90.20.21.34.15.05.96.26.87.48.10.00.00.0

us-gaap:RestrictedCashCurrent



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312015-12-31
Value228020192028203416691629165516921410162316151481125813921412
Percentage of RestrictedCashCurrent100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:RevenueRemainingPerformanceObligation



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value491503493504480457472471465
Percentage of RevenueRemainingPerformanceObligation100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementBusinessSegments

ajg:BrokerageSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value278337327333309284297294288
Percentage of RevenueRemainingPerformanceObligation56.766.966.266.264.562.262.862.561.9

ajg:RiskManagementSegment



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-31
Value79166166170170173175177177
Percentage of RevenueRemainingPerformanceObligation16.333.133.833.835.537.837.237.538.1

us-gaap:AwardType

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized

us-gaap:PerformanceShares



Period End2020-03-122019-03-142018-09-302018-06-302018-03-312018-03-152017-09-302017-06-302017-03-312017-03-162016-03-172016-03-112015-03-112014-05-122014-03-12
Value82500.073600.078200.078200.078200.078200.086250.086250.086250.086250.072900.072900.053900.048800.048800.0
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:PlanName

us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant

ajg:LongTermIncentivePlan



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302011-12-31
Value111313131314141414161616244447777999588881010106
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:TitleOfIndividual, us-gaap:PlanName

srt:Officer, ajg:LongTermIncentivePlan



Period End2020-03-122019-03-142018-03-15
Value111
Percentage of ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant0.00.00.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-30
Value322232222222322232223223
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

ajg:Range01



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value100000111222211222222122222100012
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions33.315.012.518.518.842.947.851.950.080.077.879.381.281.879.282.181.2100.0100.083.386.773.171.465.60.00.00.00.00.00.00.00.00.0

ajg:Range02



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312016-12-312016-09-302016-06-302016-03-312015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value10000000000001111100011
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions51.520.020.818.521.918.220.817.918.816.713.326.928.634.40.00.00.00.00.00.00.00.00.0

ajg:Range03



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312015-03-312014-12-312014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value011111111000000000100011
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions15.265.066.763.059.452.452.248.150.020.022.220.718.80.00.00.00.00.00.00.00.00.00.00.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-30
Value97889899910101111101010118899889
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

ajg:Range01



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value100000111222322233322222222112023
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions20.02.54.84.66.510.212.114.614.324.525.226.428.622.322.925.727.736.437.124.228.927.427.927.80.00.00.00.00.00.00.00.00.0

ajg:Range02



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value111222222244411113333222222122022
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions18.924.122.623.023.726.125.324.024.524.542.140.940.214.615.214.714.340.940.433.030.929.830.232.20.00.00.00.00.00.00.00.00.0

ajg:Range03



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value112222233311122221112111111222022
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions16.724.125.026.426.931.831.931.231.634.917.817.317.025.224.823.923.221.621.320.920.620.219.818.90.00.00.00.00.00.00.00.00.0

ajg:Range04



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-03-312013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value111111111111133330021111112012
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions13.319.017.917.216.118.217.616.716.316.015.015.514.337.937.135.834.81.11.122.019.622.622.10.00.00.00.00.00.00.0

ajg:Range05



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-06-302012-03-31
Value111111111111111910
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions13.315.214.313.812.913.613.213.513.321.10.00.00.00.00.00.00.00.0

ajg:Range06



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312014-03-312013-12-312013-09-302013-06-302013-03-312012-09-302012-06-302012-03-31
Value111119888901010
Percentage of ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions17.815.215.514.914.00.00.00.00.00.00.00.00.0

us-gaap:SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-30
Value47.045.0344.9244.8144.6842.8442.5942.2242.1637.8137.7637.5437.2832.3732.1931.831.5528.5428.5228.4628.2726.9126.9627.19
Percentage of SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRange

ajg:Range01



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value43.7139.1739.1739.1739.1738.238.0837.9237.8935.4735.4435.2335.0130.6530.5130.1729.9428.5428.5126.9526.9925.7625.825.7925.8325.8625.8824.7624.3424.2724.2724.1823.97
Percentage of SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice193.087.087.287.487.789.289.489.889.993.893.993.893.994.794.894.994.9100.0100.094.795.595.795.794.90.00.00.00.00.00.00.00.00.0

ajg:Range02



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312016-12-312016-09-302016-06-302016-03-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value46.4343.7143.7143.7143.7139.1239.1339.1539.1535.9535.6535.6429.8329.8629.7129.5829.4329.4427.6127.5327.0226.9426.9226.92
Percentage of SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice198.897.197.397.597.8120.9121.6123.1124.1126.1125.3126.1110.9110.8109.30.00.00.00.00.00.00.00.00.0

ajg:Range03



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312015-03-312014-12-312014-03-312013-12-312013-09-302013-06-302013-03-312012-12-312012-09-302012-06-302012-03-31
Value56.8646.5446.5646.5646.5646.6146.6146.6146.6246.8746.8746.8746.870.00.032.3432.9732.9529.7729.829.1129.1129.129.12
Percentage of SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1121.0103.4103.7103.9104.2108.8109.4110.4110.6124.0124.1124.9125.70.00.00.00.00.00.00.00.00.00.00.0

us-gaap:ShortTermBorrowings



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312014-09-302014-06-302014-03-312013-12-312013-09-302013-03-312012-12-312012-06-302012-03-312011-12-31
Value45562049042536036523023536029012536869557860828535524515315511514014725346763023550129489210
Percentage of ShortTermBorrowings100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-312012-12-31
Value507052154912494749584569461245134584416441723910372736553741365536523688370737113219330521141672
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:StatementEquityComponents

us-gaap:AccumulatedOtherComprehensiveIncome



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-312012-12-31
Value-1231-759-925-802-721-785-673-651-499-559-498-661-699-763-620-603-535-522-496-338-380-260-2-32
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest-24.3-14.6-18.8-16.2-14.6-17.2-14.6-14.4-10.9-13.4-12.0-16.9-18.8-20.9-16.6-16.5-14.7-14.2-13.4-9.1-11.8-7.9-0.1-2.0

us-gaap:AdditionalPaidInCapital



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-312012-12-31
Value390938253697365636063541351634463405338833663323328032653239319132023209319330912722264913581055
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest77.173.475.373.972.777.576.276.474.381.480.785.088.089.386.687.387.787.086.183.384.680.264.263.1

us-gaap:CommonStock



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-312012-12-31
Value189188186186185184183182182181180180179178177177177176176174166164133125
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest3.73.63.83.83.74.04.04.04.04.34.34.64.84.94.84.84.84.84.84.75.25.06.37.5

us-gaap:NoncontrollingInterest



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-312012-12-31
Value406068687770686969596265645954555549557374752914
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest0.81.21.41.41.61.51.51.51.51.41.51.71.71.61.51.51.51.41.52.02.32.31.40.8

us-gaap:RetainedEarnings



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312016-09-302016-06-302016-03-312015-12-312015-09-302015-06-302015-03-312014-12-312013-12-312012-12-31
Value216119011884183918101558151714661426109510621002901916889835753774778710636676596510
Percentage of StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest42.636.538.437.236.534.132.932.531.126.325.525.624.225.123.822.820.621.021.019.219.820.528.230.5

us-gaap:UnamortizedDebtIssuanceExpense



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-312017-09-302017-06-302017-03-312016-12-312015-12-31
Value767776675665553
Percentage of UnamortizedDebtIssuanceExpense100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

us-gaap:UnbilledContractsReceivable



Period End2020-03-312019-12-312019-09-302019-06-302019-03-312018-12-312018-09-302018-06-302018-03-312017-12-31
Value797556675703767496587608682415
Percentage of UnbilledContractsReceivable100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

Line plots across dimensions of each concept

us-gaap:IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest us-gaap:ConsolidationItems, us-gaap:StatementBusinessSegments


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


us-gaap:Goodwill us-gaap:StatementBusinessSegments


us-gaap:Goodwill us-gaap:StatementGeographical


us-gaap:Goodwill us-gaap:StatementGeographical, us-gaap:StatementBusinessSegments


us-gaap:Goodwill us-gaap:StatementGeographical, us-gaap:StatementBusinessSegments


us-gaap:IntangibleAssetsNetExcludingGoodwill us-gaap:FiniteLivedIntangibleAssetsByMajorClass


us-gaap:LongTermDebt us-gaap:LineOfCreditFacility, us-gaap:ShortTermDebtType


us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap:StatementEquityComponents


us-gaap:ProfitLoss us-gaap:StatementEquityComponents