v3.25.2
Investments - Summary of Fair Value and Amortized Costs (Details) - USD ($)
$ in Millions
Jun. 30, 2025
Dec. 31, 2024
Schedule of Investments [Line Items]    
Amortized Cost, net $ 5,847.4 $ 5,842.5
Fair Value 5,453.3 5,387.9
Fixed maturity securities    
Schedule of Investments [Line Items]    
Amortized Cost, net 5,847.4 5,842.5
Gross Unrealized Gains 60.4 48.4
Gross Unrealized Losses 454.5 503.0
Fair Value 5,453.3 5,387.9
Mortgage-backed securities    
Schedule of Investments [Line Items]    
Amortized Cost, net 643.5 827.9
Gross Unrealized Gains 5.5 2.7
Gross Unrealized Losses 43.5 74.8
Fair Value 605.5 755.8
Other, including U.S. Treasury securities    
Schedule of Investments [Line Items]    
Amortized Cost, net 424.4 426.5
Gross Unrealized Gains 0.7 0.1
Gross Unrealized Losses 61.5 69.0
Fair Value 363.6 357.6
Municipal bonds    
Schedule of Investments [Line Items]    
Amortized Cost, net 1,240.0 1,239.1
Gross Unrealized Gains 17.5 17.5
Gross Unrealized Losses 105.6 105.8
Fair Value 1,151.9 1,150.8
Foreign government bonds    
Schedule of Investments [Line Items]    
Amortized Cost, net 14.1 14.1
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.8 1.0
Fair Value 13.3 13.1
Corporate bonds    
Schedule of Investments [Line Items]    
Amortized Cost, net 1,955.1 1,995.2
Gross Unrealized Gains 24.2 17.3
Gross Unrealized Losses 208.5 230.1
Fair Value 1,770.8 1,782.4
Other asset-backed securities    
Schedule of Investments [Line Items]    
Amortized Cost, net 1,570.3 1,339.7
Gross Unrealized Gains 12.5 10.8
Gross Unrealized Losses 34.6 22.3
Fair Value $ 1,548.2 $ 1,328.2