Investments (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
The credit portion of other-than-temporary impairments on fixed maturity securities, non-credit portion of an impairment has been recognized in other comprehensive income (loss)
Beginning Balance	$ 187	$ 143	$ 99
Additional credit impairments on:
Previously impaired securities	5	44	44
Securities without prior impairments	2	8	9
Reductions-disposals	(2)	(8)	(9)
Ending Balance	$ 192	$ 187	$ 143