Net Income per Common Share (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
BASIC NET INCOME PER COMMON SHARE
Average Number of Common Shares Outstanding (in shares)	201,263,646	207,248,094	208,309,331
Net Income	$ 2,031.1	$ 1,107.3	$ 1,336.0
Less: Dividends on Preferred Stock	41.8	41.8	41.8
Net Income Applicable to Common Stock	1,989.3	1,065.5	1,294.2
Less: Earnings Allocated to Participating Securities	16.9	11.6	11.8
Earnings Allocated to Common Shares Outstanding	$ 1,972.4	$ 1,053.9	$ 1,282.4
Basic Net Income Per Common Share (in dollars per share)	$ 9.80	$ 5.09	$ 6.16
DILUTED NET INCOME PER COMMON SHARE
Average Number of Common Shares Outstanding (in shares)	201,263,646	207,248,094	208,309,331
Plus Dilutive Effect of Share-based Compensation (in shares)	606,459	315,652	557,933
Average Common and Potential Common Shares (in shares)	201,870,105	207,563,746	208,867,264
Earnings Allocated to Common and Potential Common Shares	$ 1,972.3	$ 1,053.9	$ 1,282.4
Diluted Net Income Per Common Share (in dollars per share)	$ 9.77	$ 5.08	$ 6.14
Common stock equivalents not included in the computation of diluted earnings per share because their inclusion would have been antidilutive (in shares)	100,000	100,000