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Investment Securities - Narrative (Details) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2024 USD ($) Investments | Sep. 30, 2023 USD ($) | Sep. 30, 2024 USD ($) Investments | Sep. 30, 2023 USD ($) | Dec. 31, 2023 USD ($) Investments
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss | $ 0.7 |  | $ 0.7 |  | $ 0.8
Interest Receivable | 127.3 |  | 127.3 |  | 129.1
Debt Securities, Available-for-sale, Realized Gain | 0.0 | $ 0.0 |  |  |
Debt Securities, Available-for-sale, Realized Loss | 0.0 | 0.0 |  | $ (23.5) |
Callable structured notes amortized costs | 0.0 |  | 0.0 |  |
Securities Sold under Agreements to Repurchase, Fair Value of Collateral | 3,159.8 |  | 3,159.8 |  | 3,858.6
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure | $ 2,888.0 |  | $ 2,888.0 |  | $ 3,462.2
Investment securities in an unrealized loss position (securities) | Investments | 648 |  | 648 |  | 704
Debt Securities, Current |  | 853.0 |  | 853.0 |
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Amortized Cost Basis | $ 1,514.6 |  | $ 1,514.6 |  |
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Fair Value | 1,478.0 |  | 1,478.0 |  |
Accrued interest reversal | (0.4) | $ (1.0) | (2.4) | $ (1.9) |
Debt Securities |  |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |
Interest Receivable | $ 33.1 |  | $ 33.1 |  | $ 38.5

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