Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Numerator
Net Income	$ 335.6	$ 389.5	$ 524.7	$ 784.7
Denominator
Weighted Average Common Shares - Basic	174,110,900	189,894,100	176,142,600	191,302,500
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	321,000.0	435,200	456,000.0	576,000.0
Weighted Average Common Shares - Assuming Dilution	174,431,900	190,329,300	176,598,600	191,878,500
Net Income Per Common Share
Basic	$ 1.93	$ 2.05	$ 2.98	$ 4.10
Assuming Dilution	$ 1.92	$ 2.05	$ 2.97	$ 4.09