Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net other-than-temporary impairment losses recognized in earnings	$ 64	$ 77	$ 114	$ 180
Corporate and other bonds [Member]
Net other-than-temporary impairment losses recognized in earnings	7	49	23	73
States, municipalities and political subdivisions [Member]
Net other-than-temporary impairment losses recognized in earnings	17		17
Residential mortgage-backed [Member]
Net other-than-temporary impairment losses recognized in earnings	20	21	49	95
Other asset-backed [Member]
Net other-than-temporary impairment losses recognized in earnings		4		4
Total asset-backed [Member]
Net other-than-temporary impairment losses recognized in earnings	20	25	49	99
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Net other-than-temporary impairment losses recognized in earnings			1
Total fixed maturity securities available-for-sale [Member]
Net other-than-temporary impairment losses recognized in earnings	44	74	90	172
Common stock [Member]
Net other-than-temporary impairment losses recognized in earnings	1	3	5	7
Preferred stock [Member]
Net other-than-temporary impairment losses recognized in earnings	19		19	1
Total equity securities available-for-sale [Member]
Net other-than-temporary impairment losses recognized in earnings	$ 20	$ 3	$ 24	$ 8