Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share [Abstract]
Net income	$ 177.2	$ 170.0	$ 260.8	$ 254.2
Weighted average number of shares outstanding, basic (in shares)	35.6	37.4	36.0	37.7
Add: Potential effect of dilutive securities attributable to stock-based payments	0.1	0.3	0.1	0.3
Weighted-average shares outstanding – diluted	35.7	37.7	36.1	38.0
Earnings per share, basic (in dollars per share)	$ 4.97	$ 4.55	$ 7.25	$ 6.74
Earnings per share, diluted (in dollars per share)	$ 4.96	$ 4.51	$ 7.23	$ 6.70