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v3.25.1

Investments - Summary of Fixed Maturities (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Cost or Amortized Cost | $ 5,147.0 | $ 4,438.3
Fair Market Value | 4,978.3 | 4,231.1
Fixed income securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Due one year or less, Cost or Amortized Cost | 834.1 | 512.0
Due one year or less, Fair Market Value | 831.2 | 505.8
Due after one year through five years, Cost or Amortized Cost | 2,386.5 | 2,889.0
Due after one year through five years, Fair Market Value | 2,353.2 | 2,818.9
Due after five years through ten years, Cost or Amortized Cost | 1,060.7 | 495.1
Due after five years through ten years, Fair Market Value | 1,008.7 | 440.3
Due after ten years, Cost or Amortized Cost | 3.5 | 15.7
Due after ten years, Fair Market Value | 3.4 | 15.2
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost | 4,284.8 | 3,911.8
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value | 4,196.5 | 3,780.2
Non-agency commercial mortgage-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Amortized Cost | 5.0 | 6.6
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value | 4.4 | 5.8
Cost or Amortized Cost | 5.0 | 6.6
Fair Market Value | 4.4 | 5.8
Agency mortgage-backed |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Amortized Cost | 600.8 | 519.9
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value | 518.7 | $ 445.1
Asset backed securities and privately held asset backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Amortized Cost | 256.4 |
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value | $ 258.7 |

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