Consolidated Balance Sheet (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Available-for-sale securities, amortized cost	$ 37,973.7	$ 37,948.5
Held to maturity, fair value	20,399.1	23,315.4
Unearned income	$ 9.7	$ 10.4
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Common stock, par value (in dollars per share)	$ 1.6667	$ 1.6667
Common stock, authorized (in shares)	560,000,000	560,000,000
Common stock, outstanding (in shares)	208,379,813	207,761,875
Treasury stock (in shares)	36,791,711	37,409,649
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