Net Income Per Common Share Computations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net income from continuing operations	$ 249.1	$ 13.3	$ 139.6
Net loss attributable to noncontrolling interest	0.0	(0.2)	(0.3)
Net income from continuing operations, net of loss attributable to noncontrolling interests	249.1	13.5	139.9
Net loss from discontinued operations	0.0	(95.4)	(2.4)
Numerator for basic net income (loss) per common share	249.1	(81.9)	137.5
Numerator for diluted net income from continuing operations per common share	249.1	13.5	139.9
Numerator for diluted net income (loss) per common share	$ 249.1	$ (81.9)	$ 137.5
Denominator for net income (loss) per common share:
Basic (in shares)	38.6	39.6	40.1
Plus dilutive effect of stock awards (in shares)	0.6	0.5	0.5
Diluted (in shares)	39.2	40.1	40.6
Basic
Continuing operations (in dollars per share)	$ 6.45	$ 0.34	$ 3.49
Discontinued operations (in dollars per share)	0	(2.41)	(0.06)
Net income (loss) per common share - basic (in dollars per share)	6.45	(2.07)	3.43
Diluted
Continuing operations (in dollars per share)	6.35	0.33	3.44
Discontinued operations (in dollars per share)	0	(2.41)	(0.06)
Net income (loss) per common share - diluted (in dollars per share)	$ 6.35	$ (2.08)	$ 3.38