Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Interest Income
Federal Reserve and Other Central Bank Deposits	$ 459.7	$ 377.0
Interest-Bearing Due from and Deposits with Banks	34.6	28.2
Federal Funds Sold	0.0	0.2
Securities Purchased under Agreements to Resell	823.9	125.9
Securities — Taxable	445.3	337.8
Securities - Non-Taxable	0.3	0.3
Loans	653.6	578.2
Other Interest-Earning Assets	28.2	7.8
Total Interest Income	2,445.6	1,455.4
Interest Expense
Deposits	881.7	564.6
Federal Funds Purchased	33.6	40.1
Securities Sold Under Agreements to Repurchase	813.9	116.1
Other Borrowings	88.6	135.0
Senior Notes	44.1	39.2
Long-Term Debt	55.6	29.2
Total Interest Expense	1,917.5	924.2
Net Interest Income	$ 528.1	$ 531.2