Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Interest Income
Loans and Leases	$ 256.4	$ 172.2	$ 447.6	$ 344.2
Securities — Taxable	195.4	165.7	366.2	339.6
Securities - Non-Taxable	0.3	0.4	0.7	0.8
Interest-Bearing Due from and Deposits with Banks	6.5	2.7	9.1	5.1
Federal Reserve and Other Central Bank Deposits and Other	66.2	2.1	84.7	3.3
Total Interest Income	524.8	343.1	908.3	693.0
Interest Expense
Deposits	23.2	(14.8)	7.3	(28.2)
Federal Funds Purchased	2.8	(0.5)	2.8	(0.4)
Securities Sold Under Agreements to Repurchase	6.0	0.0	6.3	0.0
Other Borrowings	8.4	3.2	11.5	6.7
Senior Notes	18.9	13.8	28.5	27.5
Long-Term Debt	6.8	5.3	12.2	10.6
Floating Rate Capital Debt	0.0	0.5	0.0	1.1
Total Interest Expense	66.1	7.5	68.6	17.3
Net Interest Income	$ 458.7	$ 335.6	$ 839.7	$ 675.7