Earnings Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator:
Net income (loss)	$ 114.2	$ 0.8	$ 121.2	$ (35.9)
Preferred stock dividends	2.6	2.6	5.2	5.2
Net income (loss) available to common shareholders - basic and diluted	$ 111.6	$ (1.8)	$ 116.0	$ (41.1)
Denominator:
Weighted average common shares outstanding - basic	208.5	206.9	208.2	204.8
Stock-based compensation arrangements	0.9	0	1.0	0
Weighted average common shares outstanding - diluted	209.4	206.9	209.2	204.8
Basic earnings (loss) per common share	$ 0.54	$ (0.01)	$ 0.56	$ (0.20)
Diluted earnings (loss) per common share	$ 0.53	$ (0.01)	$ 0.55	$ (0.20)
Stock Compensation Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	3.2		3.5
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	4.5	4.5	4.5	4.5