Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Interest Income
Federal Reserve and Other Central Bank Deposits	$ 457.6	$ 398.9	$ 917.3	$ 775.9
Interest-Bearing Due from and Deposits with Banks	31.4	32.1	66.0	60.3
Federal Funds Sold	0.0	0.1	0.0	0.3
Securities Purchased under Agreements to Resell	863.5	284.3	1,687.4	410.2
Securities — Taxable	477.4	366.3	922.7	704.1
Securities - Non-Taxable	0.3	0.4	0.6	0.7
Loans	648.3	639.2	1,301.9	1,217.4
Other Interest-Earning Assets	28.0	13.7	56.2	21.5
Total Interest Income	2,506.5	1,735.0	4,952.1	3,190.4
Interest Expense
Deposits	898.3	633.5	1,780.0	1,198.1
Federal Funds Purchased	38.7	87.6	72.3	127.7
Securities Sold Under Agreements to Repurchase	851.5	273.4	1,665.4	389.5
Other Borrowings	95.3	156.5	183.9	291.5
Senior Notes	44.1	42.1	88.2	81.3
Long-Term Debt	55.7	30.4	111.3	59.6
Total Interest Expense	1,983.6	1,223.5	3,901.1	2,147.7
Net Interest Income	$ 522.9	$ 511.5	$ 1,051.0	$ 1,042.7