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Investments - Contractual Maturities of Bonds (Details) - USD ($) $ in Millions | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Cost or Amortized Cost |  |
Due in one year or less | $ 257.8 |
Due after one year through five years | 387.6 |
Due after five years through ten years | 0.0 |
Due after ten years | 0.0 |
Cost or Amortized Cost | 645.4 | $ 673.5
Fair Value |  |
Due in one year or less | 252.9 |
Due after one year through five years | 380.5 |
Due after five years through ten years | 0.0 |
Due after ten years | 0.0 |
Fair Value | $ 633.4 | $ 650.3

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