Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	$ 216	$ 232	$ 1,352
Corporate and other bonds [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	95	68	357
States, municipalities and political subdivisions [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings		62	79
Residential mortgage-backed [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	105	71	461
Commercial mortgage-backed [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings		3	193
Other asset-backed [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	6	3	31
Total asset-backed [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	111	77	685
Redeemable preferred stock [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings			9
Total fixed maturity securities available-for-sale [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	206	207	1,130
Common stock [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	8	11	5
Preferred stock [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	1	14	217
Total equity securities available-for-sale [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	9	25	222
Short term investments [Member]
Net OTTI Losses
Net other-than-temporary impairment losses recognized in earnings	$ 1