v3.25.1
Investments - Schedule of Aging of Unrealized Losses on Company's Investments in Fixed Maturities, Equity Securities and Other Investments (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Schedule of Investments [Line Items]    
Fair Value, Less Than One Year $ 83.9 $ 117.0
Unrealized Losses, Less Than One Year 1.7 2.8
Fair Value, One Year or Greater 11.4 9.7
Unrealized Losses, One Year or Greater 0.2 0.3
Fair Value, Total 95.3 126.7
Unrealized Losses, Total 1.9 3.1
U.S. Governments    
Schedule of Investments [Line Items]    
Fair Value, Less Than One Year 17.7 17.4
Unrealized Losses, Less Than One Year 0.3 0.6
Fair Value, One Year or Greater 0.0 0.0
Unrealized Losses, One Year or Greater 0.0 0.0
Fair Value, Total 17.7 17.4
Unrealized Losses, Total 0.3 0.6
Corporate bonds    
Schedule of Investments [Line Items]    
Fair Value, Less Than One Year 24.1 19.6
Unrealized Losses, Less Than One Year 1.1 1.2
Fair Value, One Year or Greater 2.5 1.7
Unrealized Losses, One Year or Greater 0.1 0.1
Fair Value, Total 26.6 21.3
Unrealized Losses, Total 1.2 1.3
Commercial mortgage-backed securities    
Schedule of Investments [Line Items]    
Fair Value, Less Than One Year 28.3 9.7
Unrealized Losses, Less Than One Year 0.2 0.1
Fair Value, One Year or Greater 8.9 8.0
Unrealized Losses, One Year or Greater 0.1 0.2
Fair Value, Total 37.2 17.7
Unrealized Losses, Total 0.3 0.3
Residential mortgage-backed securities    
Schedule of Investments [Line Items]    
Fair Value, Less Than One Year   48.9
Unrealized Losses, Less Than One Year   0.6
Fair Value, One Year or Greater   0.0
Unrealized Losses, One Year or Greater   0.0
Fair Value, Total   48.9
Unrealized Losses, Total   0.6
Asset-backed securities    
Schedule of Investments [Line Items]    
Fair Value, Less Than One Year 13.8 9.9
Unrealized Losses, Less Than One Year 0.1 0.1
Fair Value, One Year or Greater 0.0 0.0
Unrealized Losses, One Year or Greater 0.0 0.0
Fair Value, Total 13.8 9.9
Unrealized Losses, Total $ 0.1 0.1
Collateralized loan obligations    
Schedule of Investments [Line Items]    
Fair Value, Less Than One Year   11.5
Unrealized Losses, Less Than One Year   0.2
Fair Value, One Year or Greater   0.0
Unrealized Losses, One Year or Greater   0.0
Fair Value, Total   11.5
Unrealized Losses, Total   $ 0.2