Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Interest Income
Loans and Leases	$ 200.9	$ 183.9
Securities - Taxable	103.3	76.6
Securities - Non-Taxable	1.1	1.3
Interest-Bearing Due from and Deposits with Banks	23.7	26.6
Federal Reserve Deposits and Other	23.0	10.4
Total Interest Income	352.0	298.8
Interest Expense
Deposits	22.2	16.7
Federal Funds Purchased	0.3	0.2
Securities Sold Under Agreements to Repurchase	0.4	0.1
Other Borrowings	2.7	1.2
Senior Notes	11.7	11.6
Long-Term Debt	6.1	7.8
Floating Rate Capital Debt	0.8	0.6
Total Interest Expense	44.2	38.2
Net Interest Income	$ 307.8	$ 260.6