Investments (Details 37) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	$ 588	$ 492	$ 338
Interest Income Recognized - Cash Basis	9	11	8
Interest Income Recognized - Accrual Basis	2	3	1
Commercial mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	313	192
Interest Income Recognized - Cash Basis	5	5
Interest Income Recognized - Accrual Basis	1	1
Agricultural mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	252	284
Interest Income Recognized - Cash Basis	4	6
Interest Income Recognized - Accrual Basis	1	2
Residential mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	23	16
Interest Income Recognized - Cash Basis	0	0
Interest Income Recognized - Accrual Basis	$ 0	$ 0

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The average recorded investment related to impaired financing receivables.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=6965416&loc=d3e5212-111524

-Subparagraph (c)(1)

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=6965416&loc=d3e5258-111524

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- Definition

The interest income recognized during the time within that period that the financing receivables were impaired.

+ References

+ Details

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- Definition

The interest income recognized on a cash-basis method of accounting during the time within that period that the financing receivables were impaired.

+ References

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