Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

+ Details

Name:	us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

+ References

+ Details

Name:	us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeInstrumentsGainLossLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624177-113959

+ Details

Name:	us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

+ Details

Name:	us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

+ Details

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNetAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as a liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624163-113959

+ Details

Name:	us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Net Increase or Decrease in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

+ Details

Name:	us-gaap_EmbeddedDerivativeGainLossOnEmbeddedDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_InvestmentIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=gac_PolicyholdersFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=gac_InterestRateFutureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=gac_RealizedInvestmentGainsLossesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=gac_FuturesOnEquityIndicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwaptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_OtherContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CurrencySwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_FairValueHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivative Financial Instruments (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	$ 26,847	$ 54,684
Net investment income
Derivatives not designated as hedging instruments
Change in fair value of GLWB	10,450	2,770
Policyholders' Funds
Derivatives not designated as hedging instruments
Embedded derivatives - GLWB	21,707		$ 11,257
Interest rate swaps \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	10,622	2,822
Interest rate futures \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(204)	(151)
Interest rate futures \| Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(32)	135
Futures on equity indices \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(230)	147
Futures on equity indices \| Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(1,441)	(723)
Interest rate swaptions \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	134	910
Interest rate swaptions \| Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(195)	(987)
Other forward contracts \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	3,056	16,825
Other forward contracts \| Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	2,938	(9,340)
Cross-currency swaps \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	12,199	45,046
Cash flow hedges:
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)	(1,604)	17,155
Gain (loss) reclassified from OCI into net income (Effective portion)	2,486	2,258
Cash flow hedges: \| Interest rate swaps
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)	525	3,141
Cash flow hedges: \| Interest rate swaps \| Net investment income
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) reclassified from OCI into net income (Effective portion)	1,494	1,856
Cash flow hedges: \| Interest rate futures
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)	0	0
Cash flow hedges: \| Interest rate futures \| Net investment income
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) reclassified from OCI into net income (Effective portion)	0	(21)
Cash flow hedges: \| Cross-currency swaps
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)	(2,129)	14,014
Cash flow hedges: \| Cross-currency swaps \| Net investment income
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) reclassified from OCI into net income (Effective portion)	992	423
Fair value hedges:
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income	0	(808)
Gain (loss) on hedged assets recognized in net income	0	813
Fair value hedges: \| Interest rate swaps \| Net investment income
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income	0	(1,438)
Gain (loss) on hedged assets recognized in net income	0	1,443
Fair value hedges: \| Interest rate swaps \| Realized investment gains (losses)
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income	0	630
Gain (loss) on hedged assets recognized in net income	$ 0	$ (630)