v3.26.1
Investments - Fair Value and Gross Unrealized Losses (Details)
$ in Millions
Jun. 30, 2026
USD ($)
Jun. 30, 2026
security
Jun. 30, 2026
Jun. 30, 2026
position
Dec. 31, 2025
USD ($)
Dec. 31, 2025
security
Dec. 31, 2025
Dec. 31, 2025
position
Fixed maturity securities, Gross Unrealized Losses                
Number of positions with a gross unrealized loss, 12 months or less (security) | security   759       466    
Number of positions with a gross unrealized loss, more than 12 months (security)   1,565   1,565   1,649   1,649
Number of positions with a gross unrealized loss, total (security) | security   2,324       2,115    
Fair value as a percentage of total fixed maturities and equity securities fair value, 12 months or less (percent)     23.00%       14.90%  
Fair value as a percentage of total fixed maturities and equity securities fair value, more than 12 months (percent)     39.20%       42.50%  
Fair value as a percentage of total fixed maturities and equity securities fair value, total (percent)     62.20%       57.40%  
Fixed maturity securities                
Fixed maturity securities, Fair Value                
Fixed maturity securities, fair value, 12 months or less $ 1,325.9       $ 849.6      
Fixed maturity securities, fair value, more than 12 months 2,262.7       2,429.8      
Fixed maturity securities, fair value, total 3,588.6       3,279.4      
Fixed maturity securities, Gross Unrealized Losses                
Fixed maturity securities, gross unrealized losses, 12 months or less 27.4       15.2      
Fixed maturity securities, gross unrealized losses, more than 12 months 383.1       371.0      
Fixed maturity securities, gross unrealized losses, total 410.5       386.2      
Mortgage-backed securities                
Fixed maturity securities, Fair Value                
Fixed maturity securities, fair value, 12 months or less 174.5       69.7      
Fixed maturity securities, fair value, more than 12 months 225.5       247.9      
Fixed maturity securities, fair value, total 400.0       317.6      
Fixed maturity securities, Gross Unrealized Losses                
Fixed maturity securities, gross unrealized losses, 12 months or less 2.3       0.3      
Fixed maturity securities, gross unrealized losses, more than 12 months 39.9       38.3      
Fixed maturity securities, gross unrealized losses, total 42.2       38.6      
Other                
Fixed maturity securities, Fair Value                
Fixed maturity securities, fair value, 12 months or less 38.7       27.1      
Fixed maturity securities, fair value, more than 12 months 273.3       276.1      
Fixed maturity securities, fair value, total 312.0       303.2      
Fixed maturity securities, Gross Unrealized Losses                
Fixed maturity securities, gross unrealized losses, 12 months or less 0.9       0.4      
Fixed maturity securities, gross unrealized losses, more than 12 months 57.7       55.7      
Fixed maturity securities, gross unrealized losses, total 58.6       56.1      
Municipal bonds                
Fixed maturity securities, Fair Value                
Fixed maturity securities, fair value, 12 months or less 108.4       126.0      
Fixed maturity securities, fair value, more than 12 months 584.1       596.4      
Fixed maturity securities, fair value, total 692.5       722.4      
Fixed maturity securities, Gross Unrealized Losses                
Fixed maturity securities, gross unrealized losses, 12 months or less 2.0       2.8      
Fixed maturity securities, gross unrealized losses, more than 12 months 80.8       79.9      
Fixed maturity securities, gross unrealized losses, total 82.8       82.7      
Foreign government bonds                
Fixed maturity securities, Fair Value                
Fixed maturity securities, fair value, 12 months or less 0.0       0.0      
Fixed maturity securities, fair value, more than 12 months 6.9       9.0      
Fixed maturity securities, fair value, total 6.9       9.0      
Fixed maturity securities, Gross Unrealized Losses                
Fixed maturity securities, gross unrealized losses, 12 months or less 0.0       0.0      
Fixed maturity securities, gross unrealized losses, more than 12 months 0.7       0.6      
Fixed maturity securities, gross unrealized losses, total 0.7       0.6      
Corporate bonds                
Fixed maturity securities, Fair Value                
Fixed maturity securities, fair value, 12 months or less 600.1       387.3      
Fixed maturity securities, fair value, more than 12 months 887.3       930.6      
Fixed maturity securities, fair value, total 1,487.4       1,317.9      
Fixed maturity securities, Gross Unrealized Losses                
Fixed maturity securities, gross unrealized losses, 12 months or less 18.9       10.5      
Fixed maturity securities, gross unrealized losses, more than 12 months 180.9       171.6      
Fixed maturity securities, gross unrealized losses, total 199.8       182.1      
Other asset-backed securities                
Fixed maturity securities, Fair Value                
Fixed maturity securities, fair value, 12 months or less 404.2       239.5      
Fixed maturity securities, fair value, more than 12 months 285.6       369.8      
Fixed maturity securities, fair value, total 689.8       609.3      
Fixed maturity securities, Gross Unrealized Losses                
Fixed maturity securities, gross unrealized losses, 12 months or less 3.3       1.2      
Fixed maturity securities, gross unrealized losses, more than 12 months 23.1       24.9      
Fixed maturity securities, gross unrealized losses, total $ 26.4       $ 26.1