Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Interest Income
Federal Reserve and Other Central Bank Deposits		$ 472.1	$ 11.3	$ 28.8
Interest-Bearing Due from and Deposits with Banks		46.6	9.1	22.4
Securities Purchased under Agreements to Resell		103.7	3.5	3.9
Securities – Taxable		899.9	658.8	801.2
Securities - Non-Taxable		1.3	1.5	1.4
Loans and Leases		1,344.3	713.5	774.6
Other Interest-Earning Assets		9.8	8.8	11.2
Total Interest Income	$ 1,643.5	2,877.7	1,406.5	1,643.5
Interest Expense
Deposits		602.8	(61.3)	48.4
Federal Funds Purchased		34.1	(0.4)	2.2
Securities Sold under Agreements to Repurchase		90.7	0.2	1.0
Other Borrowings		126.2	14.2	45.3
Senior Notes		92.7	48.3	72.7
Long-Term Debt		44.0	21.1	26.5
Floating Rate Capital Debt		0.0	1.7	4.2
Total Interest Expense	$ 200.3	990.5	23.8	200.3
Net Interest Income		$ 1,887.2	$ 1,382.7	$ 1,443.2