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Investment Securities - Cost and Amortized Cost Maturity Schedule (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
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Fixed Maturities, Excluding Asset-Backed Securities And Collateralized Loan Obligations |  |
Cost or Amortized Cost |  |
Due in one year or less | $ 319.9 |
Due after one year through five years | 845.0 |
Due after five years through ten years | 303.4 |
Due after ten years | 101.7 |
Carrying Value |  |
Due in one year or less | 315.0 |
Due after one year through five years | 813.9 |
Due after five years through ten years | 287.0 |
Due after ten years | 94.9 |
Mortgage and asset-backed securities and collateralized loan obligations |  |
Cost or Amortized Cost |  |
Mortgage and asset-backed securities and collateralized loan obligations | 628.4 |
Carrying Value |  |
Mortgage and asset-backed securities and collateralized loan obligations | 598.5 |
Fixed maturity investments |  |
Cost or Amortized Cost |  |
Total fixed maturity investments | 2,198.4 | $ 2,076.0
Carrying Value |  |
Total fixed maturity investments | $ 2,109.3 | $ 1,920.9

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