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, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share [Abstract]
Net income	$ 245.9	$ 217.2	$ 370.2	$ 315.2
Weighted average number of shares outstanding, basic (in shares)	35.6	35.5	35.6	35.5
Add: Potential effect of dilutive securities attributable to stock-based payments	0.2	0.1	0.2	0.1
Weighted-average shares outstanding – diluted	35.8	35.6	35.8	35.6
Earnings per share - Basic (in dollars per share)	$ 6.91	$ 6.12	$ 10.40	$ 8.88
Earnings per share - Diluted (in dollars per share)	$ 6.87	$ 6.10	$ 10.34	$ 8.85