Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator
Net Income	$ 395.2	$ 358.3
Denominator
Weighted Average Common Shares - Basic	192,550,200	198,111,200
Dilution for Assumed Exercises of Nonvested Stock Awards	716,900	1,408,900
Weighted Average Common Shares - Assuming Dilution	193,267,100	199,520,100
Net Income Per Common Share
Basic	$ 2.05	$ 1.81
Assuming Dilution	$ 2.04	$ 1.80