Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, authorized (shares)	800,000,000	800,000,000
Common stock, issued (shares)	543,116,260	543,116,271
Common stock held in treasury at cost (shares)	145,068,954	145,087,054
Other borrowed funds, fair value (less than)	$ 100.0	$ 100.0
Other liabilities, fair value	100.0	100.0
Preferred stock, par value	0.5	0.5
Portion at Fair Value, Fair Value Disclosure
Loans held for sale, fair value	700.0	700.0
Loans, fair value	1,200.0	1,200.0
Other assets, fair value	$ 100.0	$ 100.0