Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net income	$ 60.4	$ 7.0
Preferred stock dividends	2.6	2.6
Net income applicable to common shareowners - basic and diluted	$ 57.8	$ 4.4
Denominator:
Weighted average common shares outstanding - basic	42.1	42.0
Stock-based compensation arrangements	0.2	0.1
Weighted average common shares outstanding - diluted	42.3	42.1
Basic and diluted earnings per common share	$ 1.37	$ 0.10
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	0.2	0.6
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	0.9	0.9