Employee Benefit Plans - Share-Based Compensation Expense (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-Based Compensation Expense
Recurring amortization	$ 9	$ 7	$ 6
Accelerated amortization for retirement eligible employees	0	0	1
Recorded in share-based compensation, after the effects of DAC	9.0	7.0	7.0
Employee Stock Purchase Plan Expense	0ago_EmployeeStockPurchasePlanExpense	0ago_EmployeeStockPurchasePlanExpense	0ago_EmployeeStockPurchasePlanExpense
Total Share‑Based Cost	10	8	8
Less: Share‑based compensation capitalized as DAC	0	0	1
Share‑based compensation expense	10	8	7
Income tax benefit	2	2	2
Employee [Member]
Share-Based Compensation Expense
Total Share‑Based Cost	9	7	7
Directors [Member}
Share-Based Compensation Expense
Total Share‑Based Cost	$ 1	$ 1	$ 1

Employee Stock Purchase Plan Expense

No definition available.

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- Definition

Share Based and Employee Stock Purchase Plan Expense

+ References

No definition available.

+ Details

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- Definition

Share Based and Employee Stock Purchase Plan Expense, Net of Capitalized Costs

+ References

No definition available.

+ Details

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- Definition

Represents the amount of accelerated amortization of share-based compensation cost for retirement eligible employees.

+ References

No definition available.

+ Details

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

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- Definition

Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ 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 (h)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ 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 (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.

+ References

No definition available.

+ Details

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