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Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Millions | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Available-for-Sale, Amortized Cost |  |
Available-for-Sale Amortized Cost, Within One Year | $ 63.7 |
Available-for-Sale Amortized Cost, After One Year but Within Five Years | 1,307.6 |
Available-for-Sale Amortized Cost, After Five Years but Within Ten Years | 1,148.0 |
Available-for-Sale Amortized Cost, After Ten Years | 3,574.0 |
Amortized Cost | 6,093.3 | $ 6,307.8
Available-for-Sale, Estimated Fair Value |  |
Available-for-Sale Estimated Fair Value, Within One Year | 62.7 |
Available-for-Sale Estimated Fair Value, After One Year but Within Five Years | 1,213.5 |
Available-for-Sale Estimated Fair Value, After Five Years but Within Ten Years | 1,044.3 |
Available-for-Sale Estimated Fair Value, After Ten Years | 3,282.6 |
Estimated Fair Value | 5,603.1 | 5,841.5
Held-to-Maturity, Amortized Cost |  |
Held-to-Maturity Amortized Cost, Within One Year | 2.5 |
Held-to-Maturity Amortized Cost, After One Year but Within Five Years | 430.7 |
Held-to-Maturity Amortized Cost, After Five Years but Within Ten Years | 557.3 |
Held-to-Maturity Amortized Cost, After Ten Years | 1,808.7 |
Amortized Cost1 | 2,799.2 | 3,208.7
Held-to-Maturity, Estimated Fair Value |  |
Held-to-Maturity Estimated Fair Value, Within One Year | 2.5 |
Held-to-Maturity Estimated Fair Value, After One Year but Within Five Years | 404.0 |
Held-to-Maturity Estimated Fair Value, After Five Years but Within Ten Years | 487.0 |
Held-to-Maturity Estimated Fair Value, After Ten Years | 1,546.9 |
Investment debt securities held-to-maturity | 2,440.4 | 2,874.0
Securities Sold under Agreements to Repurchase [Abstract] |  |
Securities Sold under Agreements to Repurchase, Fair Value of Collateral | 4,391.6 | 3,858.6
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure | 3,902.1 | $ 3,462.2
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Fair Value | 1,541.6 |
Investment Securities, Primarily Classified As Available-For-Sale, Callable, Within One Year, Amortized Cost Basis | $ 1,595.1 |

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