Preferred Securities (Details) (Preferred Stock [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Preferred Stock [Member]
Preferred Stock (Numeric) [Line Items]
Shares authorized	10	10	10
Dividend requirements on noncontrolling interests	$ 16	$ 17	$ 18