Subsequent Events (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Series A Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock, dividends	$ 7	$ 6	$ 7	$ 6	$ 7	$ 6	$ 7	$ 6	$ 7	$ 6	$ 7	$ 6	$ 26	$ 26	$ 26
Series B Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock, dividends	24	24	24	24	24	24	24	24	24	24	24	24	96	96	96
Subsequent Event [Member] | Dividend Declared [Member] | Series A Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock, dividend rate													$ 0.2527777
Preferred stock, dividends													6
Subsequent Event [Member] | Dividend Declared [Member] | Series B Preferred Stock [Member]
Subsequent Event [Line Items]
Preferred stock, dividend rate													$ 0.4062500
Preferred stock, dividends													$ 24