Net Interest Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Interest Income
Federal Reserve and Other Central Bank Deposits	$ 328.8	$ 436.4	$ 692.3	$ 816.4
Interest-Bearing Due from and Deposits with Banks	18.2	21.8	37.7	45.2
Federal Funds Sold and Securities Purchased under Agreements to Resell	783.6	693.2	1,610.5	1,380.0
Securities — Taxable	517.6	462.2	1,005.1	917.2
Securities - Non-Taxable	0.2	0.3	0.4	0.6
Loans	517.1	576.3	1,029.3	1,151.2
Other Interest-Earning Assets	23.8	22.6	48.1	43.1
Total Interest Income	2,189.3	2,212.8	4,423.4	4,353.7
Interest Expense
Deposits	565.0	722.0	1,156.9	1,423.9
Federal Funds Purchased	19.6	24.4	40.9	48.0
Securities Sold Under Agreements to Repurchase	769.8	680.6	1,574.2	1,353.8
Other Borrowings	79.9	80.4	155.4	160.1
Senior Notes	41.2	39.0	82.3	77.8
Long-Term Debt	38.3	55.9	84.2	111.5
Total Interest Expense	1,513.8	1,602.3	3,093.9	3,175.1
Net Interest Income	$ 675.5	$ 610.5	$ 1,329.5	$ 1,178.6