Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Interest Income
Loans and Leases	$ 201.3	$ 171.0	$ 402.2	$ 354.9
Securities - Taxable	96.9	77.2	200.1	153.7
Securities - Non-Taxable	1.6	1.2	2.8	2.6
Interest-Bearing Due from and Deposits with Banks	16.5	22.7	34.0	42.8
Federal Reserve and Other Central Bank Deposits	28.4	16.7	57.6	33.6
Total Interest Income	344.7	288.8	696.7	587.6
Interest Expense
Deposits	21.2	18.4	43.4	35.1
Federal Funds Purchased	0.3	0.1	0.6	0.3
Securities Sold Under Agreements to Repurchase	0.6	0.1	1.0	0.2
Other Borrowings	4.0	1.1	6.7	2.3
Senior Notes	11.7	11.9	23.4	23.5
Long-Term Debt	6.4	5.5	12.5	13.3
Floating Rate Capital Debt	0.8	0.5	1.6	1.1
Total Interest Expense	45.0	37.6	89.2	75.8
Net Interest Income	$ 299.7	$ 251.2	$ 607.5	$ 511.8