Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2024		Sep. 30, 2023	Sep. 30, 2024		Sep. 30, 2023
Numerator
Net Income	$ 645.7		$ 202.0	$ 1,430.4		$ 953.2
Denominator
Weighted Average Common Shares - Basic	186,400,700		196,083,200	189,665,100		197,289,500
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	481,700		1,048,600	544,600		1,005,600
Weighted Average Common Shares - Assuming Dilution	186,882,400		197,131,800	190,209,700		198,295,100
Net Income Per Common Share
Basic	$ 3.46		$ 1.03	$ 7.54		$ 4.83
Assuming Dilution	$ 3.46		$ 1.02	$ 7.52		$ 4.81
Cost of Shares Repurchased	$ 202.0	[1]	$ 74.8	$ 504.8	[1]	$ 175.4

[1] 1Includes a de minimis amount of commissions for the three and nine months ended September 30, 2024 and a de minimis amount and $0.1 million of commissions for the three and nine months ended September 30, 2023, respectively. Also includes $2.0 million and $4.8 million of excise tax for the three and nine months ended September 30, 2024, respectively, and $0.7 million and $1.2 million of excise tax for the three and nine months ended September 30, 2023, respectively.