Investments (Details 24) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	$ 2	$ 47	$ 17	$ 53
Equity Securities [Member]
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	(2)	(47)	(17)	(53)
Non-redeemable preferred stock [Member]
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	0	38	0	38
Common Stock
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	2	9	17	15
Perpetual hybrid securities [Member]
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	0	38	0	38
Other industries [Member]
Entity Sector Industry Classifications [Abstract]
Equity securities other than temporary impairment losses recognized in earnings	$ 2	$ 9	$ 17	$ 15