Claim and Claim Adjustment Expense Reserves - Narratives (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] | ||||
| Loss from catastrophes, net of reinsurance | $ 78 | $ 41 | $ 226 | $ 200 |
| Catastrophe-related reinsurance reinstatement premiums | 0 | 0 | 9 | 0 |
| Pretax (favorable) unfavorable development | (1) | (1) | 190 | 190 |
| 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 | (1) | (1) | 93 | 56 |
| Other insurance operations | ||||
| Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] | ||||
| Pretax (favorable) unfavorable development | $ 0 | $ 0 | $ 97 | $ 134 |