Investments (details) - OTTI Rollforward (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 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	$ 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	14	9
Reductions due to sales/defaults of credit-impaired securities	(4)	(16)
Adjustments to book value of credit-impaired securities due to changes in cash flows	5	3
Cumulative OTTI credit losses recognized for securities still held, end of period	152	135
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	47	46
Additions for OTTI securities where credit losses have been previously recognized	12	4
Reductions due to sales/defaults of credit-impaired securities		(3)
Adjustments to book value of credit-impaired securities due to changes in cash flows	(1)
Cumulative OTTI credit losses recognized for securities still held, end of period	58	47
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	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	2	5
Reductions due to sales/defaults of credit-impaired securities	(4)	(13)
Adjustments to book value of credit-impaired securities due to changes in cash flows	6	3
Cumulative OTTI credit losses recognized for securities still held, end of period	$ 94	$ 88