Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator
Net Income	$ 824.2	$ 793.0	$ 1,100.3
Denominator
Weighted Average Common Shares - Basic	204,232,900	203,642,000	209,728,900
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	615,000.0	113,300	125,500
Weighted Average Common Shares - Assuming Dilution	204,847,900	203,755,300	209,854,400
Net Income Per Common Share
Basic	$ 4.04	$ 3.89	$ 5.25
Assuming Dilution	$ 4.02	$ 3.89	$ 5.24