Investments (details) - OTTI Rollforward (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
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 other comprehensive income [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	$ 152	$ 135
Additions for OTTI securities where no credit losses were previously recognized		2
Additions for OTTI securities where credit losses have been previously recognized	8	14
Reductions due to sales/defaults of credit-impaired securities	(1)	(4)
Adjustments to book value of credit-impaired securities due to changes in cash flows	6	5
Cumulative OTTI credit losses recognized for securities still held, end of period	165	152
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 other comprehensive income [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	58	47
Additions for OTTI securities where credit losses have been previously recognized	4	12
Reductions due to sales/defaults of credit-impaired securities	(1)
Adjustments to book value of credit-impaired securities due to changes in cash flows	2	(1)
Cumulative OTTI credit losses recognized for securities still held, end of period	63	58
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 other comprehensive income [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	94	88
Additions for OTTI securities where no credit losses were previously recognized		2
Additions for OTTI securities where credit losses have been previously recognized	4	2
Reductions due to sales/defaults of credit-impaired securities		(4)
Adjustments to book value of credit-impaired securities due to changes in cash flows	4	6
Cumulative OTTI credit losses recognized for securities still held, end of period	$ 102	$ 94