Net Income Per Common Share Computations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Income (loss) from continuing operations, net of tax	$ 43.1	$ 15.2	$ (3.1)	$ 135.4
Net loss attributable to noncontrolling interest	(0.1)	0.0	(0.2)	0.0
Net income (loss) from continuing operations, net of loss attributable to noncontrolling interests	43.2	15.2	(2.9)	135.4
Loss from discontinued operations, net of tax	0.0	(0.4)	(96.1)	(1.9)
Numerator for basic net income (loss) per common share	43.2	14.8	(99.0)	133.5
Numerator for diluted net income (loss) from continuing operations per common share	43.2	15.2	(2.9)	135.4
Numerator for diluted net income (loss) per common share	$ 43.2	$ 14.8	$ (99.0)	$ 133.5
Denominator for net income (loss) per common share:
Basic (in shares)	39.5	40.0	39.6	40.2
Plus dilutive effect of stock awards (in shares)	0.6	0.7	0.0	0.5
Diluted (in shares)	40.1	40.7	39.6	40.7
Net (loss) income per common share data, basic:
Continuing operations (in dollars per share)	$ 1.09	$ 0.38	$ (0.07)	$ 3.37
Discontinued operations (in dollars per share)	0	(0.01)	(2.43)	(0.05)
Net (loss) income per common share data - basic (in dollars per share)	1.09	0.37	(2.50)	3.32
Net (loss) income per common share data, diluted:
Continuing operations (in dollars per share)	1.08	0.37	(0.07)	3.33
Discontinued operations (in dollars per share)	0	(0.01)	(2.43)	(0.05)
Net (loss) income per common share data - diluted (in dollars per share)	$ 1.08	$ 0.36	$ (2.50)	$ 3.28
Anti-dilutive stock awards excluded from the calculation of diluted shares (in shares)	0.0	0.0	0.6	0.0