Stockholders' Equity (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Preferred stock	Sep. 30, 2011 Preferred stock	Jun. 30, 2011 Preferred stock	Mar. 30, 2011 Preferred stock	Dec. 31, 2010 Preferred stock	Sep. 30, 2010 Preferred stock	Jun. 30, 2010 Preferred stock	Mar. 31, 2010 Preferred stock	Dec. 31, 2009 Preferred stock	Sep. 30, 2009 Preferred stock	Jun. 30, 2009 Preferred stock	Mar. 31, 2009 Preferred stock
Preferred Stock
Preferred stock, authorized (in shares)			13.0	13.0
Dividends to preferred stockholders	$ 33.0	$ 33.0	$ 33.0	$ 8.3	$ 8.2	$ 8.3	$ 8.2	$ 8.3	$ 8.2	$ 8.3	$ 8.2	$ 8.3	$ 8.2	$ 8.3	$ 8.2