Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Interest Income
Loans and Leases	$ 298.2	$ 252.0
Securities — Taxable	277.5	177.8
Securities - Non-Taxable	1.1	2.0
Interest-Bearing Due from and Deposits with Banks	17.9	19.9
Federal Reserve and Other Central Bank Deposits and Other	68.1	54.2
Total Interest Income	662.8	505.9
Interest Expense
Deposits	147.6	63.1
Federal Funds Purchased	13.4	5.3
Securities Sold Under Agreements to Repurchase	1.8	2.7
Other Borrowings	49.9	26.5
Senior Notes	15.9	11.8
Long-Term Debt	10.0	11.0
Floating Rate Capital Debt	2.2	1.5
Total Interest Expense	240.8	121.9
Net Interest Income	$ 422.0	$ 384.0