Contracts Accounted for as Financial Guaranty Insurance - Reconciliation of Net Expected Loss to be Paid and Expensed (Details) - USD ($) $ in Millions |
Sep. 30, 2026 |
Jun. 30, 2026 |
Dec. 31, 2025 |
Sep. 30, 2025 |
Jun. 30, 2025 |
Dec. 31, 2024 |
|---|---|---|---|---|---|---|
| Guarantor Obligations [Line Items] | ||||||
| Net expected loss to be paid (recovered) - Financial guaranty insurance | $ 113 | $ 192 | $ 101 | $ 104 | $ 186 | $ 106 |
| Net expected loss to be expensed (present value) | 294 | |||||
| Financial Guarantee Insurance And Other Product Line | ||||||
| Guarantor Obligations [Line Items] | ||||||
| Net expected loss to be paid (recovered) - Financial guaranty insurance | 101 | |||||
| Contra-paid, net | 22 | |||||
| Salvage and subrogation recoverable, net | 450 | |||||
| Loss and LAE reserve - Financial guaranty insurance contracts, net of reinsurance | (279) | |||||
| Net expected loss to be expensed (present value) | $ 294 |