Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (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	$ 464.0	$ 356.3	$ 408.7
Net loss from discontinued operations	0.0	0.8	0.1
Income from continuing operations	$ 464.0	$ 357.1	$ 408.8
Weighted-average shares outstanding - basic (in shares)	37.2	38.3	39.0
Add: Potential effect of diluted securities attributable to stock-based payments	0.3	0.3	0.4
Weighted-average shares outstanding - diluted (in shares)	37.5	38.6	39.4
Earnings per share – Basic:
Income from continuing operations (in usd per share)	$ 12.47	$ 9.32	$ 10.49
Loss from discontinued operations (in usd per share)	0	(0.02)	0
Net income (in usd per share)	12.47	9.30	10.49
Earnings per share – Diluted:
Income from continuing operations (in usd per share)	12.39	9.26	10.38
Loss from discontinued operations (in usd per share)	0	(0.02)	0
Net income (in usd per share)	$ 12.39	$ 9.24	$ 10.38