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Investment Securities - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025 USD ($) Investments	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) Investments	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($) Investments
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 0.7		$ 0.7		$ 0.9
Interest Receivable	106.6		106.6		116.8
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	2,877.5		2,877.5		3,460.2
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	$ 2,664.0		$ 2,664.0		$ 3,092.6
Investment securities in an unrealized loss position (securities) | Investments	633		633		670
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Amortized Cost Basis	$ 682.2		$ 682.2
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Fair Value	654.1		654.1
Accrued interest reversal	(0.4)	$ (0.4)	(2.9)	$ (2.4)
Debt Securities
Schedule of Held-to-maturity Securities [Line Items]
Interest Receivable	$ 23.2		$ 23.2		$ 29.6

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