Earnings Per Common Share - Computation of EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ (1.6)	$ 18.8	$ 77.6	$ 7.0	$ 30.5	$ 79.3	$ 180.7	$ 0.3	$ 101.8	$ 290.8	$ 117.7
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	0.3	0.0	0.0	0.0	2.1	1.0	10.9	48.9	0.3	62.9	(42.1)
Numerator:
Net income (loss)	$ (1.3)	$ 18.8	$ 77.6	$ 7.0	$ 32.6	$ 80.3	$ 191.6	$ 49.2	102.1	353.7	75.6
Preferred stock dividends									10.4	10.4	10.4
Net Income (Loss) Available to Common Stockholders, Basic and Diluted									$ 91.7	$ 343.3	$ 65.2
Weighted Average Number of Shares Outstanding, Basic									42.0	41.9	41.7
Denominator:
Stock-based compensation arrangements									0.1	0.1	0.2
Weighted Average Number of Shares Outstanding, Diluted									42.1	42.0	41.9
Earnings Per Share, Basic and Diluted Share									$ 2.18
Income (Loss) from Continuing Operations, Per Basic Share	$ (0.10)	$ 0.39	$ 1.79	$ 0.10	$ 0.66	$ 1.83	$ 4.25	$ (0.06)	2.17	$ 6.69
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0.01	0.00	0.00	0.00	0.05	0.02	0.26	1.17	0.01	1.50
Earnings Per Share, Basic	(0.09)	0.39	1.79	0.10	0.71	1.85	4.51	1.11	2.18	8.19	$ 1.56
Income (Loss) from Continuing Operations, Per Diluted Share	(0.10)	0.38	1.78	0.10	0.66	1.83	4.15	(0.06)	2.17	6.68
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0.01	0.00	0.00	0.00	0.05	0.02	0.26	1.17	0.01	1.49
Earnings Per Share, Diluted	$ (0.09)	$ 0.38	$ 1.78	$ 0.10	$ 0.71	$ 1.85	$ 4.41	$ 1.11	$ 2.18	$ 8.17	$ 1.56
Continuing Operations [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									$ 101.8	$ 290.8	$ 117.7
Numerator:
Preferred stock dividends									10.4	10.4	10.4
Net Income (Loss) Available to Common Stockholders, Basic and Diluted									$ 91.4	$ 280.4	$ 107.3
Denominator:
Income (Loss) from Continuing Operations, Per Basic Share and Diluted Share									$ 2.17
Income (Loss) from Continuing Operations, Per Basic Share									2.17	$ 6.69	$ 2.57
Income (Loss) from Continuing Operations, Per Diluted Share									$ 2.17	$ 6.68	$ 2.56
Discontinued Operations [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									$ 0.3	$ 62.9	$ (42.1)
Numerator:
Preferred stock dividends									0.0	0.0	0.0
Net Income (Loss) Available to Common Stockholders, Basic and Diluted									$ 0.3	$ 62.9	$ (42.1)
Denominator:
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share and Diluted Share									$ 0.01
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share									0.01	$ 1.50	$ (1.01)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share									$ 0.01	$ 1.49	$ (1.00)