Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share [Abstract]
Net income	$ 239.0	$ 130.4	$ 609.2	$ 445.6
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	0.2	0.2	0.1
Weighted-average shares outstanding – diluted	35.8	35.7	35.8	35.6
Earnings per share - Basic (in dollars per share)	$ 6.71	$ 3.67	$ 17.11	$ 12.55
Earnings per share - Diluted (in dollars per share)	$ 6.68	$ 3.65	$ 17.02	$ 12.51