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, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net income	$ 83.6	$ 84.2
Weighted average number of shares outstanding, basic (in shares)	36.3	38.0
Add: Potential effect of dilutive securities attributable to stock-based payments	0.2	0.2
Weighted-average shares outstanding – diluted	36.5	38.2
Earnings per share, basic (in dollars per share)	$ 2.30	$ 2.22
Earnings per share, diluted (in dollars per share)	$ 2.29	$ 2.20