Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income	$ 84.2	$ 12.9
Exclude: Income from discontinued operations	0.0	(0.4)
Income from continuing operations	$ 84.2	$ 12.5
Weighted-average shares outstanding – basic	38.0	38.4
Add: Potential effect of dilutive securities attributable to stock-based payments	0.2	0.3
Weighted-average shares outstanding – diluted	38.2	38.7
Earnings per share – Basic:
Income from continuing operations (in dollars per share)	$ 2.22	$ 0.33
Loss from discontinued operations (in dollars per share)	0	0.01
Net income (in dollars per share)	2.22	0.34
Earnings per share – Diluted:
Income from continuing operations (in dollars per share)	2.20	0.32
Loss from discontinued operations (in dollars per share)	0	0.01
Net income (in dollars per share)	$ 2.20	$ 0.33