Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net other-than-temporary impairment losses recognized in earnings	$ 154	$ 216	$ 232
Corporate and other bonds [Member]
Net other-than-temporary impairment losses recognized in earnings	27	95	68
States, municipalities and political subdivisions [Member]
Net other-than-temporary impairment losses recognized in earnings	34		62
Residential mortgage-backed [Member]
Net other-than-temporary impairment losses recognized in earnings	50	105	71
Commercial mortgage-backed [Member]
Net other-than-temporary impairment losses recognized in earnings			3
Other asset-backed [Member]
Net other-than-temporary impairment losses recognized in earnings		6	3
Total asset-backed [Member]
Net other-than-temporary impairment losses recognized in earnings	50	111	77
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	112	206	207
Common stock [Member]
Net other-than-temporary impairment losses recognized in earnings	6	8	11
Preferred stock [Member]
Net other-than-temporary impairment losses recognized in earnings	36	1	14
Total equity securities available-for-sale [Member]
Net other-than-temporary impairment losses recognized in earnings	42	9	25
Short term investments [Member]
Net other-than-temporary impairment losses recognized in earnings		$ 1