Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Net income	$ 124.3	$ 98.0
Weighted average number of shares outstanding, basic (in shares)	35.6	35.5
Add: Potential effect of dilutive securities attributable to stock-based payments	0.2	0.1
Weighted-average shares outstanding – diluted	35.8	35.6
Earnings per share - Basic (in dollars per share)	$ 3.49	$ 2.76
Earnings per share - Diluted (in dollars per share)	$ 3.47	$ 2.75