v3.26.1
Investments - Summary of Fixed Maturities (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]    
Cost or Amortized Cost $ 5,106.0 $ 5,147.0
Fair Market Value 5,109.3 4,978.3
Fixed income securities    
Debt Securities, Available-for-sale [Line Items]    
Due one year or less, Cost or Amortized Cost 257.6 834.1
Due one year or less, Fair Market Value 257.5 831.2
Due after one year through five years, Cost or Amortized Cost 2,095.2 2,386.5
Due after one year through five years, Fair Market Value 2,103.8 2,353.2
Due after five years through ten years, Cost or Amortized Cost 1,390.4 1,060.7
Due after five years through ten years, Fair Market Value 1,402.9 1,008.7
Due after ten years, Cost or Amortized Cost 97.1 3.5
Due after ten years, Fair Market Value 97.2 3.4
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost 3,840.3 4,284.8
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value 3,861.4 4,196.5
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 9.8 5.0
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value 9.5 4.4
Cost or Amortized Cost 9.8 5.0
Fair Market Value 9.5 4.4
Agency mortgage-backed    
Debt Securities, Available-for-sale [Line Items]    
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Amortized Cost 740.6 600.8
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value 721.1 518.7
Asset backed securities    
Debt Securities, Available-for-sale [Line Items]    
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Amortized Cost 515.3 256.4
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value 517.3 $ 258.7
Privately-held investments, global corporate securities    
Debt Securities, Available-for-sale [Line Items]    
Cost or Amortized Cost 33.8  
Fair Market Value $ 34.2