Investments (details) - OTTI Rollforward (USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Roll-forward of the credit component of other-than-temporary impairments on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in accumulated other changes in equity from nonowner sources [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	$ 143	$ 130	$ 135	$ 139
Additions for OTTI securities where no credit losses were previously recognized			2
Additions for OTTI securities where credit losses have been previously recognized	5	2	10	6
Reductions due to sales/defaults of credit-impaired securities			(1)	(14)
Adjustments to book value of credit-impaired securities due to changes in cash flows	2	1	4	2
Cumulative OTTI credit losses recognized for securities still held, end of period	150	133	150	133
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Roll-forward of the credit component of other-than-temporary impairments on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in accumulated other changes in equity from nonowner sources [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	51	45	47	46
Additions for OTTI securities where credit losses have been previously recognized	4	1	8	3
Reductions due to sales/defaults of credit-impaired securities				(3)
Cumulative OTTI credit losses recognized for securities still held, end of period	55	46	55	46
All other corporate bonds [Member]
Roll-forward of the credit component of other-than-temporary impairments on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in accumulated other changes in equity from nonowner sources [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	92	85	88	93
Additions for OTTI securities where no credit losses were previously recognized			2
Additions for OTTI securities where credit losses have been previously recognized	1	1	2	3
Reductions due to sales/defaults of credit-impaired securities			(1)	(11)
Adjustments to book value of credit-impaired securities due to changes in cash flows	2	1	4	2
Cumulative OTTI credit losses recognized for securities still held, end of period	$ 95	$ 87	$ 95	$ 87

This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which a previous OTTI was recognized and the investor does not intend to sell the debt security and it is not more likely than not that the investor will be required to sell the debt security before recovery of its amortized cost basis.

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-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

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This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which no such other than temporary impairment (OTTI) was previously recognized.

+ References

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 18B

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-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.

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- Definition

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

+ References

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

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-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.

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-Publisher FASB

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- Definition

This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held due to increases in cash flows expected to be collected and recognized over the remaining life of the security.

+ References

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

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-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.

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This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security because of the sale of impaired securities during the period.

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-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.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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