Claim and Claim Adjustment Expense Reserves (Commercial - Net Prior Year Claim and Allocated Claim Adjustment Expense Reserve Development) (Details) - Commercial - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
|
| Liability for Claims and Claims Adjustment Expense [Line Items] | ||
| Commercial Auto | $ 0 | $ 50 |
| General Liability | 55 | 0 |
| Workers' Compensation | 0 | 1 |
| Property and Other | 0 | 0 |
| Total pretax (favorable) unfavorable development | $ 55 | $ 51 |