v3.26.1
Claim and Claim Adjustment Expense Reserves - Narratives (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]        
Loss from catastrophes, net of reinsurance $ 60 $ 62 $ 148 $ 159
Catastrophe-related reinsurance reinstatement premiums 0 0 9 0
Pretax (favorable) unfavorable development 91 108 191 191
Total property & casualty operations | CNA Financial        
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]        
Pretax (favorable) unfavorable development (6) (4) 94 57
Other insurance operations        
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]        
Pretax (favorable) unfavorable development $ 97 112 $ 97 $ 134
Other insurance operations | CNA Financial        
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]        
Pretax (favorable) unfavorable development   $ 112