Investments (Details 24) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	$ 9	$ 5	$ 26	$ 58
Equity Securities [Member]
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	(9)	(5)	(26)	(58)
Non-redeemable preferred stock [Member]
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	0	0	0	38
Common Stock
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	9	5	26	20
Perpetual hybrid securities [Member]
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	0	0	0	38
Other industries [Member]
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	$ 9	$ 5	$ 26	$ 20