Share-Based Compensation Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period	3 years
Cash payment in settlement of Performance Share Unit Plan Units	$ 3,988	$ 6,375
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period	5 years
Great West Lifeco Inc
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of trading days considered for determination of average closing price of common stock	20 days
Great West Lifeco Inc \| Employee and Directors Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period preceding the date of the grant, to determine exercise price of options granted	5 days
Options exercisable, term	10 years
Maximum period that retiring option holders can continue to exercise outstanding options	5 years
Granted (in shares)	973,100
Compensation expense to be recognized	$ 2,664
Great West Lifeco Inc \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares considered for valuation of each stock award	1

Represents the maximum vesting period that retiring employees can continue to vest outstanding stock options.

No definition available.

Name:	gac_EmployeeServiceShareBasedCompensationOptionsMaximumVestingPeriodUponRetirement
Namespace Prefix:	gac_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of trading days prior to the date following the last day of performance period of share-based payment awards considered for determination of average closing price of common stock.

+ References

No definition available.

+ Details

Name:	gac_ShareBasedCompensationArrangementByShareBasedPaymentAwardAverageClosingPriceOfCommonStockDeterminationNumberOfTradingDaysConsidered
Namespace Prefix:	gac_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the period preceding the date of the grant of options considered to determine the exercise price of options granted.

+ References

No definition available.

+ Details

Name:	gac_ShareBasedCompensationArrangementByShareBasedPaymentExercisePriceDeterminationPeriodPriorToGrantDateToBeConsidered
Namespace Prefix:	gac_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of shares considered for valuation of each stock award.

+ References

No definition available.

+ Details

Name:	gac_ShareBasedCompensationArrangementsByShareBasedPaymentAwardNumberOfSharesForValuationOfEachStockAward
Namespace Prefix:	gac_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

+ References

No definition available.

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cash paid related to share-based compensation liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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

- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=gac_GreatWestLifecoIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=gac_EmployeeAndDirectorsStockOptionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: