Investments (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
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	$ 192	$ 187
Additional credit impairments on:
Previously impaired securities	0	3
Securities without prior impairments	0	0
Reductions-disposals	(1)	0
Ending Balance	$ 191	$ 190