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Derivative Financial Instruments (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]    
Aggregate fair value of derivative instruments with credit-risk-related contingent features, in case of net liability position $ 102,046us-gaap_DerivativeNetLiabilityPositionAggregateFairValue $ 141,653us-gaap_DerivativeNetLiabilityPositionAggregateFairValue
Collateral related to the derivatives 57,443us-gaap_CollateralAlreadyPostedAggregateFairValue 106,110us-gaap_CollateralAlreadyPostedAggregateFairValue
Fair value of assets required to settle the derivatives in, net liability position 44,603us-gaap_AssetsNeededForImmediateSettlementAggregateFairValue  
Amount of unrestricted cash collateral to counterparties in the normal course of business 57,443us-gaap_DerivativeCollateralRightToReclaimCash 106,110us-gaap_DerivativeCollateralRightToReclaimCash
Cash collateral received 13,176us-gaap_DerivativeCollateralObligationToReturnCash 791us-gaap_DerivativeCollateralObligationToReturnCash
Net derivative gains estimated to be reclassified from accumulated other comprehensive income (loss) into net income within the next twelve months 7,128gac_DerivativeInstrumentsGainLossReclassificationFromAccumulatedOCIToIncomeEstimatedNetAmountToBeTransferredInNextTwelveMonths  
Derivative financial instruments    
Notional amount 7,462,169invest_DerivativeNotionalAmount 1,544,907invest_DerivativeNotionalAmount
Net derivatives, Fair value (21,008)us-gaap_DerivativeFairValueOfDerivativeNet (100,983)us-gaap_DerivativeFairValueOfDerivativeNet
Asset derivatives, Fair value 81,692us-gaap_DerivativeFairValueOfDerivativeAsset [1] 35,604us-gaap_DerivativeFairValueOfDerivativeAsset [1]
Liability derivatives, Fair value 102,700us-gaap_DerivativeFairValueOfDerivativeLiability [1] 136,587us-gaap_DerivativeFairValueOfDerivativeLiability [1]
Interest rate swaps    
Derivative financial instruments    
Average notional amount of the derivative instruments 416,588gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember		 340,262gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
Other forward contracts    
Derivative financial instruments    
Average notional amount of the derivative instruments 4,551,500gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_OtherContractMember		 4,217,408gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_OtherContractMember
Cross-currency swaps    
Derivative financial instruments    
Average notional amount of the derivative instruments 846,165gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember		 732,581gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
Future    
Derivative financial instruments    
Average notional amount of the derivative instruments 20,570gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_FutureMember		 21,702gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_FutureMember
Swaption    
Derivative financial instruments    
Average notional amount of the derivative instruments 278,999gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwaptionMember		 407,552gac_DerivativeAverageNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwaptionMember
Derivatives designated as hedges:    
Derivative financial instruments    
Notional amount 412,975invest_DerivativeNotionalAmount
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 436,445invest_DerivativeNotionalAmount
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Net derivatives, Fair value 35,540us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 21,574us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Asset derivatives, Fair value 35,799us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 24,526us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Liability derivatives, Fair value 259us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 2,952us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Derivatives designated as hedges: | Cash flow hedges:    
Derivative financial instruments    
Notional amount 370,425invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 358,445invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Net derivatives, Fair value 35,471us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 20,068us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Asset derivatives, Fair value 35,539us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 22,889us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Liability derivatives, Fair value 68us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 2,821us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Derivatives designated as hedges: | Cash flow hedges: | Interest rate swaps    
Derivative financial instruments    
Notional amount 184,200invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 184,200invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Net derivatives, Fair value 19,593us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 17,746us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Asset derivatives, Fair value 19,593us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 17,746us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Liability derivatives, Fair value 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Derivatives designated as hedges: | Cash flow hedges: | Cross-currency swaps    
Derivative financial instruments    
Notional amount 186,225invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 174,245invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Net derivatives, Fair value 15,878us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 2,322us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Asset derivatives, Fair value 15,946us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 5,143us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Liability derivatives, Fair value 68us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 2,821us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Derivatives designated as hedges: | Fair value hedges:    
Derivative financial instruments    
Notional amount 42,550invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 78,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Net derivatives, Fair value 69us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 1,506us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Asset derivatives, Fair value 260us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 1,637us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Liability derivatives, Fair value 191us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 131us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Derivatives designated as hedges: | Fair value hedges: | Interest rate swaps    
Derivative financial instruments    
Notional amount 42,550invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 78,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Net derivatives, Fair value 69us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 1,506us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Asset derivatives, Fair value 260us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 1,637us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Liability derivatives, Fair value 191us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1] 131us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 [1]
Derivatives not designated as hedges:    
Derivative financial instruments    
Notional amount 7,049,194invest_DerivativeNotionalAmount
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 1,108,462invest_DerivativeNotionalAmount
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Net derivatives, Fair value (56,548)us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 (122,557)us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Asset derivatives, Fair value 45,893us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 11,078us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Liability derivatives, Fair value 102,441us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 133,635us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Derivatives not designated as hedges: | Interest rate swaps    
Derivative financial instruments    
Notional amount 195,600invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 128,100invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Net derivatives, Fair value 7,206us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 4,402us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Asset derivatives, Fair value 10,527us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 6,246us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Liability derivatives, Fair value 3,321us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 1,844us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Derivatives not designated as hedges: | Futures on equity indices    
Derivative financial instruments    
Notional amount 5,932invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_FuturesOnEquityIndicesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 5,505invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_FuturesOnEquityIndicesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Net derivatives, Fair value 0us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_FuturesOnEquityIndicesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 0us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_FuturesOnEquityIndicesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Asset derivatives, Fair value 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_FuturesOnEquityIndicesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_FuturesOnEquityIndicesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Liability derivatives, Fair value 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_FuturesOnEquityIndicesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_FuturesOnEquityIndicesMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Derivatives not designated as hedges: | Interest rate futures    
Derivative financial instruments    
Notional amount 10,883invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_InterestRateFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 17,958invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_InterestRateFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Net derivatives, Fair value 0us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_InterestRateFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 0us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_InterestRateFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Asset derivatives, Fair value 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_InterestRateFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_InterestRateFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Liability derivatives, Fair value 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_InterestRateFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= gac_InterestRateFutureMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Derivatives not designated as hedges: | Interest rate swaptions    
Derivative financial instruments    
Notional amount 243,344invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwaptionMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 293,964invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwaptionMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Net derivatives, Fair value 244us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwaptionMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 271us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwaptionMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Asset derivatives, Fair value 244us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwaptionMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 271us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwaptionMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Liability derivatives, Fair value 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwaptionMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]  
Derivatives not designated as hedges: | Other forward contracts    
Derivative financial instruments    
Notional amount 5,930,500invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_OtherContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		  
Net derivatives, Fair value 16,825us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_OtherContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		  
Asset derivatives, Fair value 20,925us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_OtherContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]  
Liability derivatives, Fair value 4,100us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_OtherContractMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]  
Derivatives not designated as hedges: | Cross-currency swaps    
Derivative financial instruments    
Notional amount 662,935invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 662,935invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Net derivatives, Fair value (80,823)us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 (127,230)us-gaap_DerivativeFairValueOfDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Asset derivatives, Fair value 14,197us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] 4,561us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
Liability derivatives, Fair value $ 95,020us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] $ 131,791us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CurrencySwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
[1] The estimated fair value excludes accrued income and expense. The estimated fair value of all derivatives in an asset position is reported within other assets and the estimated fair value of all derivatives in a liability position is reported within other liabilities in the condensed consolidated balance sheets.