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Investments - Schedule of Contractual Maturity (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Amortized Cost |  |
Due in One Year or Less | $ 337.0 |
Due after One Year to Five Years | 773.5 |
Due after Five Years to Ten Years | 1,021.6 |
Due after Ten Years | 3,496.9 |
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date | 1,666.0 |
Amortized Cost | 7,295.0 | $ 7,565.8
Fair Value |  |
Due in One Year or Less | 332.3 |
Due after One Year to Five Years | 746.3 |
Due after Five Years to Ten Years | 890.0 |
Due after Ten Years | 2,903.7 |
Mortgage- and Asset-backed Securities Not Due at a Single Maturity Date | 1,537.3 |
Investments in Fixed Maturities | $ 6,409.6 | $ 6,881.9

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