Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Numerator
Net Income	$ 256.9	$ 335.6	$ 488.9	$ 524.7
Denominator
Weighted Average Common Shares - Basic	159,660,200	174,110,900	161,848,100	176,142,600
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	363,900	321,000.0	344,800	456,000.0
Weighted Average Common Shares - Assuming Dilution	160,024,100	174,431,900	162,192,900	176,598,600
Net Income Per Common Share
Basic	$ 1.61	$ 1.93	$ 3.02	$ 2.98
Assuming Dilution	$ 1.61	$ 1.92	$ 3.01	$ 2.97