Preferred Stock and Stockholders' Equity - Schedule of Dividends Declared (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended			0 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 24, 2015	Jan. 16, 2015
Class of Stock [Line Items]
Dividends declared per common share (USD per share)	$ 0.875	$ 0.75	$ 0.75	$ 0.75	$ 0.75	$ 0.75	$ 0.75	$ 0.75	$ 3.125	$ 3	$ 0
Payments of Dividends	$ 0	$ 14.2	$ 14.3	$ 14.3	$ 14.3	$ 14.3	$ 14.4	$ 14.6	$ 42.8	$ 57.6
Subsequent Event
Class of Stock [Line Items]
Dividends declared per common share (USD per share)												$ 0.875
Payments of Dividends													$ 16.6