Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator
Net Income	$ 202.0	$ 510.3	$ 953.2	$ 1,118.0
Denominator
Weighted Average Common Shares - Basic	196,083,200	200,035,300	197,289,500	201,262,300
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	1,048,600	1,614,900	1,005,600	1,256,700
Weighted Average Common Shares - Assuming Dilution	197,131,800	201,650,200	198,295,100	202,519,000
Net Income Per Common Share
Basic	$ 1.03	$ 2.55	$ 4.83	$ 5.55
Assuming Dilution	$ 1.02	$ 2.53	$ 4.81	$ 5.52