Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Available-for-sale securities, amortized cost	$ 30,620.6	$ 29,229.1
Held to maturity, fair value	19,486.9	20,654.5
Unearned income	$ 6.2	$ 6.3
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Common stock, par value (in usd per share)	$ 1.6667	$ 1.6667
Common stock, authorized (in shares)	560,000,000	560,000,000
Common stock, outstanding (in shares)	194,538,575	195,969,746
Treasury stock (in shares)	50,632,949	49,201,778
Series D Preferred Stock
Preferred stock, outstanding (in shares)	5,000	5,000
Series E Preferred Stock
Preferred stock, outstanding (in shares)	16,000	16,000