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, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Earnings Per Share [Abstract]
Net income	$ 277.6	$ 245.9	$ 397.9	$ 370.2
Weighted average number of shares outstanding, basic (in shares)	35.3	35.6	35.4	35.6
Add: Potential effect of dilutive securities attributable to stock-based payments	0.2	0.2	0.2	0.2
Weighted-average shares outstanding – diluted	35.5	35.8	35.6	35.8
Earnings per share - Basic (in dollars per share)	$ 7.86	$ 6.91	$ 11.24	$ 10.40
Earnings per share - Diluted (in dollars per share)	$ 7.82	$ 6.87	$ 11.18	$ 10.34