Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net income	$ 18.8	$ 80.3	$ 103.4	$ 321.1
Preferred stock dividends	2.6	2.6	7.8	7.8
Net income applicable to common shareowners - basic and diluted	$ 16.2	$ 77.7	$ 95.6	$ 313.3
Denominator:
Weighted average common shares outstanding - basic	42.0	41.9	42.0	41.9
Stock-based compensation arrangements	0.1	0.1	0.1	0.1
Weighted average common shares outstanding - diluted	42.1	42.0	42.1	42.0
Basic earnings per common share from continuing operations	$ 0.39	$ 1.83	$ 2.28	$ 6.03
Basic earnings per common share from discontinued operations	0.00	0.02	0.00	1.45
Basic earnings per common share	0.39	1.85	2.28	7.48
Diluted earnings per common share from continuing operations	0.38	1.83	2.27	6.01
Diluted earnings per common share from discontinued operations	0.00	0.02	0.00	1.45
Diluted earnings per common share	$ 0.38	$ 1.85	$ 2.27	$ 7.46
Continuing Operations [Member]
Numerator:
Net income	$ 18.8	$ 79.3	$ 103.4	$ 260.3
Preferred stock dividends	2.6	2.6	7.8	7.8
Net income applicable to common shareowners - basic and diluted	$ 16.2	$ 76.7	$ 95.6	$ 252.5
Denominator:
Weighted average common shares outstanding - basic	42.0	41.9	42.0	41.9
Stock-based compensation arrangements	0.1	0.1	0.1	0.1
Weighted average common shares outstanding - diluted	42.1	42.0	42.1	42.0
Discontinued Operations [Member]
Numerator:
Net income	$ 0.0	$ 1.0	$ 0.0	$ 60.8
Preferred stock dividends	0.0	0.0	0.0	0.0
Net income applicable to common shareowners - basic and diluted	$ 0.0	$ 1.0	$ 0.0	$ 60.8
Denominator:
Weighted average common shares outstanding - basic	42.0	41.9	42.0	41.9
Stock-based compensation arrangements	0.1	0.1	0.1	0.1
Weighted average common shares outstanding - diluted	42.1	42.0	42.1	42.0
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	0.7	0.4	0.7
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	0.9	0.9