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, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Earnings Per Share [Abstract]
Net income	$ 269.0	$ 273.9	$ 386.2	$ 403.5
Weighted average number of shares outstanding, basic (in shares)	34.7	35.3	34.8	35.4
Add: Potential effect of dilutive securities attributable to stock-based payments	0.1	0.2	0.1	0.2
Weighted-average shares outstanding – diluted	34.8	35.5	34.9	35.6
Earnings per share - Basic (in dollars per share)	$ 7.75	$ 7.75	$ 11.11	$ 11.39
Earnings per share - Diluted (in dollars per share)	$ 7.72	$ 7.71	$ 11.06	$ 11.34