Investments (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
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
Additional credit impairments on:
Previously impaired securities	3	7
Securities without prior impairments		1
Ending Balance	$ 190	$ 151