Investment Securities - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2025 USD ($) Investments	Mar. 31, 2024 USD ($)	Dec. 31, 2024 USD ($) Investments
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 0.8		$ 0.9
Interest Receivable	107.9		116.8
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	3,234.9		3,460.2
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	$ 2,945.8		$ 3,092.6
Investment securities in an unrealized loss position (securities) | Investments	669		670
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Amortized Cost Basis	$ 1,081.3
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Fair Value	1,043.2
Accrued interest reversal	(1.5)	$ (1.8)
Debt Securities
Schedule of Held-to-maturity Securities [Line Items]
Interest Receivable	$ 25.9		$ 29.6