Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Held to maturity, fair value	$ 14,260.4	$ 13,010.9
Total loans and leases, unearned income	$ 30.2	$ 35.5
Preferred stock, par value (in dollars per share)	$ 0	$ 0
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)	224,991,295	226,126,674
Treasury stock, (in shares)	20,180,229	19,044,850
Series C Preferred Stock
Preferred stock, outstanding (in shares)	16,000	16,000
Series D Preferred Stock
Preferred stock, outstanding (in shares)	5,000	5,000