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, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Earnings Per Share [Abstract]
Net income	$ 245.8	$ 239.0	$ 643.7	$ 609.2
Weighted average number of shares outstanding, basic (in shares)	35.1	35.6	35.3	35.6
Add: Potential effect of dilutive securities attributable to stock-based payments	0.1	0.2	0.2	0.2
Weighted-average shares outstanding – diluted	35.2	35.8	35.5	35.8
Earnings per share - Basic (in dollars per share)	$ 7.01	$ 6.71	$ 18.23	$ 17.11
Earnings per share - Diluted (in dollars per share)	$ 6.98	$ 6.68	$ 18.15	$ 17.02