v3.25.2
Investments - Allowance for Credit Loss (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Rollforward of the allowance for credit loss by major security type        
Beginning balance $ 7.0 $ 2.8 $ 18.7 $ 4.7
Additional increases (decreases) for credit losses on securities with an allowance recorded in the previous period     0.1  
Write-offs charged against allowance (4.3)   (16.2) (1.6)
Additions for credit losses not previously recorded 0.4   0.4  
Foreign currency translation adjustment   0.1 0.1 (0.2)
Ending balance 3.1 2.9 3.1 2.9
Corporate debt securities        
Rollforward of the allowance for credit loss by major security type        
Beginning balance 6.8 2.7 18.5 4.6
Additional increases (decreases) for credit losses on securities with an allowance recorded in the previous period     0.1  
Write-offs charged against allowance (4.3)   (16.2) (1.6)
Foreign currency translation adjustment   0.1 0.1 (0.2)
Ending balance 2.5 2.8 2.5 2.8
Commercial mortgage-backed securities        
Rollforward of the allowance for credit loss by major security type        
Additions for credit losses not previously recorded 0.3   0.3  
Ending balance 0.3   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 0.2 0.1 0.2 0.1
Ending balance $ 0.2 $ 0.1 $ 0.2 $ 0.1