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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Earnings Per Share [Abstract]
Net income	$ 217.2	$ 177.2	$ 315.2	$ 260.8
Weighted average number of shares outstanding, basic (in shares)	35.5	35.6	35.5	36.0
Add: Potential effect of dilutive securities attributable to stock-based payments	0.1	0.1	0.1	0.1
Weighted-average shares outstanding – diluted	35.6	35.7	35.6	36.1
Earnings per share - Basic (in dollars per share)	$ 6.12	$ 4.97	$ 8.88	$ 7.25
Earnings per share - Diluted (in dollars per share)	$ 6.10	$ 4.96	$ 8.85	$ 7.23