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Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Millions | Dec. 31, 2022 | Dec. 31, 2021
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Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity |  |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost | $ 48.8 |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost | 1,478.9 |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Amortized Cost | 1,750.0 |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost | 4,295.8 |
Amortized Cost | 7,573.5 | $ 4,859.3
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity |  |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value | 48.1 |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value | 1,419.8 |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value | 1,564.3 |
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value | 3,913.9 |
Estimated Fair Value | 6,946.1 | 4,820.5
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount |  |
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost | 2.5 |
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost | 607.6 |
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost | 732.7 |
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after 10 Years, Amortized Cost | 2,110.9 |
Amortized Cost | 3,453.7 | 1,687.6
Held-to-maturity Securities, Debt Maturities, Fair Value, Rolling Maturity |  |
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value | 2.5 |
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value | 581.6 |
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value | 639.5 |
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value | 1,828.6 |
Estimated Fair Value | 3,052.2 | 1,667.5
Available-for-sale Securities and Held-to-maturity Securities |  |
Securities sold under agreements to repurchase | 4,998.9 | 2,617.8
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure | $ 4,432.0 | $ 2,610.8

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