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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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	$ 35.1	$ 101.8	$ 290.8
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent					0.3	0.0	0.0	0.0	0.0	0.3	62.9
Numerator:
Net income	$ (16.2)	$ (11.2)	$ 2.1	$ 60.4	$ (1.3)	$ 18.8	$ 77.6	$ 7.0	35.1	102.1	353.7
Preferred stock dividends									10.4	10.4	10.4
Net Income (Loss) Available to Common Stockholders, Basic and Diluted									$ 24.7	$ 91.7	$ 343.3
Denominator:
Weighted Average Number of Shares Outstanding, Basic									42.2	42.0	41.9
Stock-based compensation arrangements									0.2	0.1	0.1
Weighted Average Number of Shares Outstanding, Diluted									42.4	42.1	42.0
Income (Loss) from Continuing Operations, Per Basic Share					$ (0.10)	$ 0.39	$ 1.79	$ 0.10		$ 2.17
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share					0.01	0.00	0.00	0.00		0.01
Earnings Per Share, Basic	$ (0.45)	$ (0.33)	$ (0.01)	$ 1.37	(0.09)	0.39	1.79	0.10	$ 0.59	2.18	$ 8.19
Income (Loss) from Continuing Operations, Per Diluted Share					(0.10)	0.38	1.78	0.10		2.17
Income from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share					0.01	0.00	0.00	0.00		0.01
Earnings Per Share, Diluted	$ (0.45)	$ (0.33)	$ (0.01)	$ 1.37	$ (0.09)	$ 0.38	$ 1.78	$ 0.10	$ 0.58	2.18	$ 8.17
Earnings Per Share, Basic and Diluted										$ 2.18
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									$ 35.1	$ 101.8	$ 290.8
Numerator:
Preferred stock dividends									10.4	10.4	10.4
Net Income (Loss) Available to Common Stockholders, Basic and Diluted									$ 24.7	$ 91.4	$ 280.4
Denominator:
Weighted Average Number of Shares Outstanding, Basic									42.2	42.0	41.9
Stock-based compensation arrangements									0.2	0.1	0.1
Weighted Average Number of Shares Outstanding, Diluted									42.4	42.1	42.0
Income (Loss) from Continuing Operations, Per Basic Share									$ 0.59		$ 6.69
Income (Loss) from Continuing Operations, Per Diluted Share									$ 0.58	$ 2.17	$ 6.68
Income (Loss) from Continuing Operations, Per Basic Share and Diluted Share										$ 2.17
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									$ 0.0	$ 0.3	$ 62.9
Numerator:
Preferred stock dividends									0.0	0.0	0.0
Net Income (Loss) Available to Common Stockholders, Basic and Diluted									$ 0.0	$ 0.3	$ 62.9
Denominator:
Weighted Average Number of Shares Outstanding, Basic									0.0	42.0	41.9
Stock-based compensation arrangements									0.0	0.1	0.1
Weighted Average Number of Shares Outstanding, Diluted									0.0	42.1	42.0
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share									$ 0.00		$ 1.50
Income from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share									$ 0.00	$ 0.01	$ 1.49
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share and Diluted Share										$ 0.01