Net Income Per Common Share Computations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Income from continuing operations, net of tax	$ 4.2	$ 15.2	$ 108.3	$ 11.9	$ 7.3	$ 58.0	$ 103.2	$ 14.1	$ 139.6	$ 182.6	$ 122.4
Net loss attributable to noncontrolling interest									0.3	0.0	0.0
Net income from continuing operations, net of loss attributable to noncontrolling interests									139.9	182.6	122.4
Net income from continuing operations allocated to participating securities									0.0	0.0	(0.1)
Net (loss) income from discontinued operations	$ (0.5)	$ (0.4)	$ (1.2)	$ (0.3)	$ 4.1	$ (1.7)	$ (0.1)	$ 167.9	(2.4)	170.2	18.1
Numerator for basic net income per common share									137.5	352.8	140.4
Numerator for diluted net income from continuing operations per common share									139.9	182.6	122.4
Numerator for diluted net income per common share									$ 137.5	$ 352.8	$ 140.5
Denominator for net income per common share:
Basic (in shares)									40.1	41.3	47.2
Plus dilutive effect of stock awards (in shares)									0.5	0.3	0.6
Plus dilutive effect of participating securities (in shares)									0.0	0.0	0.2
Diluted (in shares)									40.6	41.6	48.0
Basic
Continuing operations (in dollars per share)	$ 0.11	$ 0.38	$ 2.70	$ 0.30	$ 0.18	$ 1.43	$ 2.54	$ 0.33	$ 3.49	$ 4.42	$ 2.59
Discontinued operations (in dollars per share)	(0.01)	(0.01)	(0.03)	(0.01)	0.10	(0.04)	0	3.88	(0.06)	4.12	0.38
Net income per common share - basic (in dollars per share)	0.10	0.37	2.67	0.29	0.28	1.39	2.54	4.21	3.43	8.54	2.97
Diluted
Continuing operations (in dollars per share)	0.11	0.37	2.66	0.30	0.18	1.42	2.52	0.32	3.44	4.39	2.55
Discontinued operations (in dollars per share)	(0.01)	(0.01)	(0.03)	(0.01)	0.10	(0.04)	0	3.86	(0.06)	4.09	0.37
Net income per common share - diluted (in dollars per share)	$ 0.10	$ 0.36	$ 2.63	$ 0.29	$ 0.28	$ 1.38	$ 2.52	$ 4.18	$ 3.38	$ 8.48	$ 2.92