Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024
Basic Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	190,053,947			199,937,543			192,647,391	202,614,386
Net Income	$ 457.6	$ 421.3	$ 392.0	$ 464.9	$ 896.1	$ 214.7	$ 1,270.9	$ 1,575.7
Less: Dividends on Preferred Stock	16.2			16.2			37.1	37.1
Net Income Applicable to Common Stock	441.4			448.7			1,233.8	1,538.6
Less: Earnings Allocated to Participating Securities	4.2			3.6			11.6	13.2
Earnings Allocated to Common Shares Outstanding	$ 437.2			$ 445.1			$ 1,222.2	$ 1,525.4
Basic Net Income Per Common Share (in dollars per share)	$ 2.30			$ 2.23			$ 6.34	$ 7.53
Diluted Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	190,053,947			199,937,543			192,647,391	202,614,386
Plus: Dilutive Effect of Share-based Compensation (in shares)	946,615			611,520			833,978	517,014
Average Common and Potential Common Shares (in shares)	191,000,562			200,549,063			193,481,369	203,131,400
Earnings Allocated to Common and Potential Common Shares	$ 437.2			$ 445.1			$ 1,222.2	$ 1,525.4
Diluted Net Income Per Common Share (in dollars per share)	$ 2.29			$ 2.22			$ 6.32	$ 7.51
Common stock equivalents excluded from the computation of diluted earnings per share because their inclusion would have been antidilutive (in shares)	0			0			0	200,000