v3.26.3
Investments - Net Investment Income (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Net Investment Income [Line Items]        
Total net investment income $ 139.7 $ 119.6 $ 370.9 $ 346.3
Investment Portfolio        
Net Investment Income [Line Items]        
Investment expenses (3.4) (3.2) (8.7) (9.1)
Total net investment income 115.5 96.4 298.8 273.6
Deposit Asset on Reinsurance        
Net Investment Income [Line Items]        
Total net investment income 24.2 23.2 72.1 72.7
Fixed maturity securities | Investment Portfolio        
Net Investment Income [Line Items]        
Net investment income 76.8 71.5 223.2 202.5
Equity securities | Investment Portfolio        
Net Investment Income [Line Items]        
Net investment income 0.5 0.9 1.8 2.9
Limited partnership interests | Investment Portfolio        
Net Investment Income [Line Items]        
Net investment income 35.5 21.4 65.9 60.9
Short-term and other investments | Investment Portfolio        
Net Investment Income [Line Items]        
Net investment income $ 6.1 $ 5.8 $ 16.6 $ 16.4