Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	$ 27	$ 41
Corporate and other bonds [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	10	9
Residential mortgage-backed [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	14	28
Total asset-backed [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	14	28
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	1
Total fixed maturity securities available-for-sale [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	25	37
Common stock [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	2	3
Preferred stock [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings		1
Total equity securities available-for-sale [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	$ 2	$ 4