Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Held to Maturity, Fair value	$ 6,376.2	$ 5,227.5
Total Loans and Leases, unearned income	$ 63.5	$ 103.6
Preferred Stock, Par Value (in dollars per share)	$ 0	$ 0
Preferred Stock, Authorized (in shares)	10,000,000	10,000,000
Preferred Stock, Outstanding (in shares)	16,000	16,000
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)	226,590,921	229,293,783
Treasury Stock, (in shares)	18,580,603	15,877,741