Investments (Details 31) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	$ 268	$ 279
Evaluated collectively for credit losses	53,990	52,521
Total mortgage loans	54,258	52,800
Specific credit losses	105	88
Non-specifically identified credit losses	376	576
Valuation allowances	481	664	721	304
Mortgage loan, net of valuation allowance	53,777	52,136
Commercial mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	96	120
Evaluated collectively for credit losses	40,344	37,698
Total mortgage loans	40,440	37,818
Specific credit losses	59	36
Non-specifically identified credit losses	339	526
Valuation allowances	398	562	589	232
Mortgage loan, net of valuation allowance	40,042	37,256
Agricultural mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	159	146
Evaluated collectively for credit losses	12,970	12,605
Total mortgage loans	13,129	12,751
Specific credit losses	45	52
Non-specifically identified credit losses	36	36
Valuation allowances	81	88	115	61
Mortgage loan, net of valuation allowance	13,048	12,663
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	676	2,218
Total mortgage loans	689	2,231
Specific credit losses	1	0
Non-specifically identified credit losses	1	14
Valuation allowances	2	14	17	11
Mortgage loan, net of valuation allowance	$ 687	$ 2,217

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

-URI http://asc.fasb.org/extlink&oid=6873192&loc=d3e21338-158488

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- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953423-111524

-Subparagraph (g)

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- Definition

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

+ References

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

+ References

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

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- Definition

Reflects the aggregate carrying amount of all categories of loans and leases held in portfolio, net of unearned income and the allowance for losses on loans and leases.

+ References

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph e

-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 310

-SubTopic 10

-Section 45

-Paragraph 2

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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