v3.26.1
Investments - Allowance for Credit Loss (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Rollforward of the allowance for credit loss by major security type        
Beginning balance $ 52.2 $ 7.0 $ 26.9 $ 18.7
Additions for credit losses not previously recorded 3.2 0.4 32.9 0.4
Reductions for securities sold during the period     (0.9)  
Additional increases (decreases) for credit losses on securities with an allowance recorded in the previous period 5.0   5.8 0.1
Write-offs charged against allowance (14.9) (4.3) (19.1) (16.2)
Foreign currency translation adjustment 0.1     0.1
Ending balance 45.6 3.1 45.6 3.1
Accrued interest written off to net investment income 0.6   1.6  
U.S. government and agencies        
Rollforward of the allowance for credit loss by major security type        
Beginning balance 0.1   0.1  
Additional increases (decreases) for credit losses on securities with an allowance recorded in the previous period (0.1)   (0.1)  
Corporate debt securities        
Rollforward of the allowance for credit loss by major security type        
Beginning balance 50.1 6.8 25.0 18.5
Additions for credit losses not previously recorded 2.9   32.6  
Reductions for securities sold during the period     (0.9)  
Additional increases (decreases) for credit losses on securities with an allowance recorded in the previous period 5.0   5.6 0.1
Write-offs charged against allowance (14.5) (4.3) (18.7) (16.2)
Foreign currency translation adjustment 0.1     0.1
Ending balance 43.6 2.5 43.6 2.5
Accrued interest written off to net investment income 0.6   1.6  
Commercial mortgage-backed securities        
Rollforward of the allowance for credit loss by major security type        
Beginning balance 1.6   1.4  
Additions for credit losses not previously recorded 0.3 0.3 0.3 0.3
Additional increases (decreases) for credit losses on securities with an allowance recorded in the previous period 0.2   0.4  
Write-offs charged against allowance (0.4)   (0.4)  
Ending balance 1.7 0.3 1.7 0.3
Collateralized debt obligations        
Rollforward of the allowance for credit loss by major security type        
Additions for credit losses not previously recorded   0.1   0.1
Ending balance   0.1   0.1
Other debt obligations        
Rollforward of the allowance for credit loss by major security type        
Beginning balance 0.4 0.2 0.4 0.2
Additional increases (decreases) for credit losses on securities with an allowance recorded in the previous period (0.1)   (0.1)  
Ending balance $ 0.3 $ 0.2 $ 0.3 $ 0.2