Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 30, 2025
Basic Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	183,993,670		192,751,910		184,742,283	193,965,606
Net Income	$ 792.2	$ 525.5	$ 421.3	$ 392.0	$ 1,317.8	$ 813.3
Less: Dividends on Preferred Stock	4.7		4.7		20.9	20.9
Net Income Applicable to Common Stock	787.5		416.6		1,296.9	792.4
Less: Earnings Allocated to Participating Securities	5.3		3.8		9.8	7.4
Earnings Allocated to Common Shares Outstanding	$ 782.2		$ 412.8		$ 1,287.1	$ 785.0
Basic Net Income Per Common Share (in dollars per share)	$ 4.25		$ 2.14		$ 6.97	$ 4.05
Diluted Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	183,993,670		192,751,910		184,742,283	193,965,606
Plus: Dilutive Effect of Share-based Compensation (in shares)	896,274		622,978		967,502	776,726
Average Common and Potential Common Shares (in shares)	184,889,944		193,374,888		185,709,785	194,742,332
Earnings Allocated to Common and Potential Common Shares	$ 782.3		$ 412.8		$ 1,287.0	$ 785.0
Diluted Net Income Per Common Share (in dollars per share)	$ 4.23		$ 2.13		$ 6.93	$ 4.03