Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Numerator
Net Income	$ 370.4	$ 182.9	$ 623.9	$ 335.9
Denominator
Weighted Average Common Shares - Basic	201,151,700	204,504,500	201,888,800	204,323,100
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	1,280,000	769,300	1,077,700	686,700
Weighted Average Common Shares - Assuming Dilution	202,431,700	205,273,800	202,966,500	205,009,800
Net Income Per Common Share
Basic	$ 1.84	$ 0.89	$ 3.09	$ 1.64
Assuming Dilution	$ 1.83	$ 0.89	$ 3.07	$ 1.64
Number of Treasury Shares Repurchased	1,735,500	0	3,078,600	0