Investments (Details 31) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	$ 282	$ 268
Evaluated collectively for credit losses	53,781	53,990
Total mortgage loans	54,063	54,258
Specific credit losses	105	105
Non-specifically identified credit losses	341	376
Valuation allowances	446	481	621	664
Mortgage loan, net of valuation allowance	53,617	53,777
Commercial mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	113	96
Evaluated collectively for credit losses	40,216	40,344
Total mortgage loans	40,329	40,440
Specific credit losses	61	59
Non-specifically identified credit losses	307	339
Valuation allowances	368	398	532	562
Mortgage loan, net of valuation allowance	39,961	40,042
Agricultural mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	157	159
Evaluated collectively for credit losses	12,789	12,970
Total mortgage loans	12,946	13,129
Specific credit losses	43	45
Non-specifically identified credit losses	32	36
Valuation allowances	75	81	76	88
Mortgage loan, net of valuation allowance	12,871	13,048
Residential mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Evaluated individually for credit losses	12	13
Evaluated collectively for credit losses	776	676
Total mortgage loans	788	689
Specific credit losses	1	1
Non-specifically identified credit losses	2	1
Valuation allowances	3	2	13	14
Mortgage loan, net of valuation allowance	$ 785	$ 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

-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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