v3.26.1
Current Expected Credit Losses (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Premium Receivable, Allowance for Credit Loss [Roll Forward]          
Beginning balance of the allowance for CECL on premiums receivable $ 24.0 $ 19.9 $ 22.6 $ 19.2  
Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease) 6.7 6.7 11.9 11.0  
Premium Receivable, Allowance for Credit Loss, Writeoff (2.5) (1.9) (3.6) (3.2)  
Premium Receivable, Allowance for Credit Loss, Recovery (3.5) (2.3) (6.2) (4.6)  
Ending balance of the allowance for CECL on premiums receivable 24.7 22.4 24.7 22.4  
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]          
Beginning balance of the allowance for CECL on reinsurance recoverables 0.8 0.8 0.8 0.9  
Reinsurance Recoverable, Allowance for Credit Loss, Period Increase (Decrease) 0.0 0.0 0.0 (0.1)  
Ending balance of the allowance for CECL on reinsurance recoverables 0.8 0.8 0.8 0.8  
Accrued investment income 16.3   16.3   $ 15.5
Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward]          
Beginning balance of CECL on AFS investments 0.7 1.4 0.4 1.1  
Debt Securities, Available-for-sale, Allowance for Credit Loss, Period Increase (Decrease) 0.5 (0.1) 1.0 0.2  
Debt Securities, Available-for-sale, Allowance for Credit Loss, Securities Sold (0.1) (0.2) (0.3) (0.2)  
Ending balance of CECL on AFS investments $ 1.1 $ 1.1 $ 1.1 $ 1.1  
Financial Guarantee Insurance Contract, Premium Received over Contract Period, Premium Receivable, Weighted-Average Collection Period     1 year