Investment Securities - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2026 USD ($) Investments	Mar. 31, 2025 USD ($)	Dec. 31, 2025 USD ($) Investments
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 0.5		$ 0.5
Interest Receivable	101.3		102.6
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	2,812.0		2,983.6
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	$ 2,604.3		$ 2,781.2
Investment securities in an unrealized loss position (securities) | Investments	701		633
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Amortized Cost Basis	$ 631.7
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Fair Value	604.9
Accrued interest reversal	(0.5)	$ (1.5)
Debt Securities, Realized Gain (Loss)	0.0	$ 0.0
Allowance for Credit Losses	0.0		$ 0.0
Debt Securities
Schedule of Held-to-maturity Securities [Line Items]
Interest Receivable	$ 29.4		$ 27.8