Net Income Per Common Share Computations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net income from continuing operations	$ 16.4	$ 43.1	$ (23.6)	$ (22.6)	$ 4.2	$ 15.2	$ 108.3	$ 11.9	$ 13.3	$ 139.6	$ 182.6
Net loss attributable to noncontrolling interest									(0.2)	(0.3)	0.0
Net income from continuing operations, net of loss attributable to noncontrolling interests									13.5	139.9	182.6
Net (loss) income from discontinued operations	$ 0.7	$ 0.0	$ (95.2)	$ (0.9)	$ (0.5)	$ (0.4)	$ (1.2)	$ (0.3)	(95.4)	(2.4)	170.2
Numerator for basic net (loss) income per common share									(81.9)	137.5	352.8
Numerator for diluted net income from continuing operations per common share									13.5	139.9	182.6
Numerator for diluted net (loss) income per common share									$ (81.9)	$ 137.5	$ 352.8
Denominator for net (loss) income per common share:
Basic (in shares)									39.6	40.1	41.3
Plus dilutive effect of stock awards (in shares)									0.5	0.5	0.3
Diluted (in shares)									40.1	40.6	41.6
Basic
Continuing operations (in dollars per share)	$ 0.41	$ 1.09	$ (0.59)	$ (0.57)	$ 0.11	$ 0.38	$ 2.70	$ 0.30	$ 0.34	$ 3.49	$ 4.42
Discontinued operations (in dollars per share)	0.02	0	(2.41)	(0.02)	(0.01)	(0.01)	(0.03)	(0.01)	(2.41)	(0.06)	4.12
Net income per common share - basic (in dollars per share)	0.43	1.09	(3.00)	(0.59)	0.10	0.37	2.67	0.29	(2.07)	3.43	8.54
Diluted
Continuing operations (in dollars per share)	0.41	1.08	(0.59)	(0.57)	0.11	0.37	2.66	0.30	0.33	3.44	4.39
Discontinued operations (in dollars per share)	0.02	0	(2.41)	(0.02)	(0.01)	(0.01)	(0.03)	(0.01)	(2.41)	(0.06)	4.09
Net income per common share - diluted (in dollars per share)	$ 0.43	$ 1.08	$ (3.00)	$ (0.59)	$ 0.10	$ 0.36	$ 2.63	$ 0.29	$ (2.08)	$ 3.38	$ 8.48