v3.26.3
Short-Duration Insurance Contracts - Schedule of Reinsurance Reserve Balances (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]        
Beginning gross reserves     $ 565.2  
Claims and claim expense payments for claims occurring during:        
Ending gross reserves $ 571.3   571.3  
Property & Casualty        
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]        
Beginning gross reserves 415.4 $ 419.8 404.5 $ 420.6
Less: reinsurance recoverables 100.6 98.8 101.2 100.8
Net reserves, beginning of period 314.8 321.0 303.3 319.8
Incurred claims and claim expenses:        
Claims occurring in the current period 126.4 126.3 379.5 391.9
Increase (decrease) in estimated reserves for claims occurring in prior periods (8.0) (3.0) (19.6) (13.8)
Total claims and claim expenses incurred 118.4 123.3 359.9 378.1
Claims and claim expense payments for claims occurring during:        
Current period 98.5 99.5 222.0 239.2
Prior periods 28.7 39.2 135.2 153.1
Total claims and claim expense payments 127.2 138.7 357.2 392.3
Net reserves, end of period 306.0 305.6 306.0 305.6
Plus: reinsurance recoverables 100.1 98.7 100.1 98.7
Ending gross reserves 406.1 404.3 406.1 404.3
Group Benefits        
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]        
Beginning gross reserves 119.4 113.2 113.2 104.9
Less: reinsurance recoverables 27.7 25.8 26.5 25.2
Net reserves, beginning of period 91.7 87.4 86.7 79.7
Incurred claims and claim expenses:        
Claims occurring in the current period 13.9 15.6 59.9 52.6
Increase (decrease) in estimated reserves for claims occurring in prior periods 1.0 (2.6) (3.3) (5.2)
Total claims and claim expenses incurred 14.9 13.0 56.6 47.3
Claims and claim expense payments for claims occurring during:        
Current period 12.8 9.9 29.1 19.6
Prior periods 6.2 5.6 26.5 22.5
Total claims and claim expense payments 19.1 15.4 55.6 42.1
Net reserves, end of period 87.6 85.0 87.6 85.0
Plus: reinsurance recoverables 26.0 26.0 26.0 26.0
Ending gross reserves $ 113.6 $ 111.0 $ 113.6 $ 111.0