v3.25.4
Investments - Change in Allowance for Credit Losses on Fixed Maturities Available-for-Sale (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]    
Balance, Beginning of Year $ 10.7 $ 8.2
Additions for Securities for which No Previous Expected Credit Losses were Recognized 2.4 3.4
Reductions due to Sales (1.1) (0.8)
Net (Decrease) Increase in Allowance on Securities for which Expected Credit Losses were Previously Recognized 9.3 (0.1)
Write-Offs Charged Against Allowance (1.2)  
Balance, End of Year 20.1 10.7
States and Political Subdivisions    
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]    
Balance, Beginning of Year 0.3 0.5
Additions for Securities for which No Previous Expected Credit Losses were Recognized 0.0 0.0
Reductions due to Sales 0.0 0.0
Net (Decrease) Increase in Allowance on Securities for which Expected Credit Losses were Previously Recognized 0.1 0.2
Write-Offs Charged Against Allowance 0.0  
Balance, End of Year 0.2 0.3
Bonds and Notes    
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]    
Balance, Beginning of Year 10.4 7.7
Additions for Securities for which No Previous Expected Credit Losses were Recognized 2.4 3.4
Reductions due to Sales (1.1) (0.8)
Net (Decrease) Increase in Allowance on Securities for which Expected Credit Losses were Previously Recognized 9.4 0.1
Write-Offs Charged Against Allowance (1.2)  
Balance, End of Year $ 19.9 $ 10.4