Investments (Details 4) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	$ 733	$ 268
Evaluated collectively for credit losses	53,540	53,990
Total mortgage loans	54,273	54,258
Specific credit losses	117	105
Non-specifically identified credit losses	230	376
Valuation allowances	347	481	664	721
Mortgage loan, net of valuation allowance	53,926	53,777
Commercial mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	539	96
Evaluated collectively for credit losses	39,933	40,344
Total mortgage loans	40,472	40,440
Specific credit losses	94	59
Non-specifically identified credit losses	199	339
Valuation allowances	293	398	562	589
Mortgage loan, net of valuation allowance	40,179	40,042
Agricultural mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	181	159
Evaluated collectively for credit losses	12,662	12,970
Total mortgage loans	12,843	13,129
Specific credit losses	21	45
Non-specifically identified credit losses	31	36
Valuation allowances	52	81	88	115
Mortgage loan, net of valuation allowance	12,791	13,048
Residential mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	13	13
Evaluated collectively for credit losses	945	676
Total mortgage loans	958	689
Specific credit losses	2	1
Non-specifically identified credit losses	0	1
Valuation allowances	2	2	14	17
Mortgage loan, net of valuation allowance	$ 956	$ 687

The balance represents the amount of loans that are secured by real estate mortgages.

No definition available.

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- Definition

The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 47

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 310

-Section 45

-Paragraph 4

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

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+ References

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-Topic 310

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- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6375948&loc=d3e4428-111522

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 210

-Section S99

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