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Variable Interest Entities - Additional Information (Detail) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2022 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2022 USD ($) Entity | Dec. 31, 2021 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2021 USD ($) Entity | Dec. 31, 2020 USD ($)
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Fixed income securities, amortized cost | $ 2,041,000,000 | $ 2,041,000,000 | $ 2,041,000,000 | $ 2,041,000,000 |  |  |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 31,000,000 | 31,000,000 | 31,000,000 | 31,000,000 | $ 141,000,000 | $ 141,000,000 | $ 141,000,000 |
Available-for-sale Securities | 1,966,000,000 | 1,966,000,000 | 1,966,000,000 | 1,966,000,000 |  |  |  |
Restricted Cash | 14,000,000 | 14,000,000 | 14,000,000 | 14,000,000 | 5,000,000 | 5,000,000 | 5,000,000 | $ 13,000,000
Fair value of special purpose entities | 0 | 0 | 0 | 0 |  |  |  |
Assets | 7,973,000,000 | 7,973,000,000 | 7,973,000,000 | 7,973,000,000 | 12,303,000,000 | 12,303,000,000 | 12,303,000,000 |
Liabilities | 6,647,000,000 | 6,647,000,000 | 6,647,000,000 | 6,647,000,000 | 11,187,000,000 | 11,187,000,000 | 11,187,000,000 |
Other Investments | 568,000,000 | 568,000,000 | 568,000,000 | 568,000,000 | 690,000,000 | 690,000,000 | 690,000,000 |
Long-term debt | 639,000,000 | 639,000,000 | 639,000,000 | 639,000,000 | 2,230,000,000 | 2,230,000,000 | 2,230,000,000 |
Derivative assets | 27,000,000 | 27,000,000 | 27,000,000 | 27,000,000 | 76,000,000 | 76,000,000 | 76,000,000 |
Other assets | 84,000,000 | 84,000,000 | 84,000,000 | 84,000,000 | 68,000,000 | 68,000,000 | 68,000,000 |
Accrued interest payable | 427,000,000 | 427,000,000 | 427,000,000 | 427,000,000 | 576,000,000 | 576,000,000 | 576,000,000 |
Derivative liabilities | 38,000,000 | 38,000,000 | 38,000,000 | 38,000,000 | 95,000,000 | 95,000,000 | 95,000,000 |
Other liabilities | 163,000,000 | 163,000,000 | $ 163,000,000 | $ 163,000,000 | 133,000,000 | $ 133,000,000 | $ 133,000,000 |
Variable Interest Entity, Initial Consolidation, Gain (Loss) |  | 37,000,000 |  |  | 0 |  |  | $ 0
Number of DeConsolidated Variable Interest Entities |  |  | 0 |  |  | 0 |  | 0
Consolidated Entities [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Number of consolidated Variable Interest Entities |  |  | 3 | 9 |  | 0 | 6 |
Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Available-for-sale Securities | 1,967,000,000 | 1,967,000,000 | $ 1,967,000,000 | $ 1,967,000,000 | 3,455,000,000 | $ 3,455,000,000 | $ 3,455,000,000 |
Restricted Cash | 17,000,000 | 17,000,000 | 17,000,000 | 17,000,000 | 2,000,000 | 2,000,000 | 2,000,000 | $ 2,000,000
Assets | 4,054,000,000 | 4,054,000,000 | 4,054,000,000 | 4,054,000,000 | 6,216,000,000 | 6,216,000,000 | 6,216,000,000 |
Liabilities | 4,160,000,000 | 4,160,000,000 | 4,160,000,000 | 4,160,000,000 | 6,156,000,000 | 6,156,000,000 | 6,156,000,000 |
Loans, Unpaid principal balance | 1,977,000,000 | 1,977,000,000 | 1,977,000,000 | 1,977,000,000 | 2,363,000,000 | 2,363,000,000 | 2,363,000,000 |
Long-term Debt, Fair Value | 2,788,000,000 | 2,788,000,000 | 2,788,000,000 | 2,788,000,000 | 4,056,000,000 | 4,056,000,000 | 4,056,000,000 |
Long-term debt, Unpaid principal balance | 3,064,000,000 | 3,064,000,000 | 3,064,000,000 | 3,064,000,000 | 3,579,000,000 | 3,579,000,000 | 3,579,000,000 |
Long-term debt | 3,107,000,000 | 3,107,000,000 | 3,107,000,000 | 3,107,000,000 | 4,216,000,000 | 4,216,000,000 | 4,216,000,000 |
Financing Receivable, after Allowance for Credit Loss | 1,829,000,000 | 1,829,000,000 | 1,829,000,000 | 1,829,000,000 | 2,718,000,000 | 2,718,000,000 | 2,718,000,000 |
Derivative assets | 239,000,000 | 239,000,000 | 239,000,000 | 239,000,000 | 38,000,000 | 38,000,000 | 38,000,000 |
Other assets | 2,000,000 | 2,000,000 | 2,000,000 | 2,000,000 | 2,000,000 | 2,000,000 | 2,000,000 |
Long-term Debt, at par less amortized discount | 319,000,000 | 319,000,000 | 319,000,000 | 319,000,000 | 160,000,000 | 160,000,000 | 160,000,000 |
Derivative liabilities | 1,048,000,000 | 1,048,000,000 | 1,048,000,000 | 1,048,000,000 | 1,940,000,000 | 1,940,000,000 | 1,940,000,000 |
Other liabilities | 5,000,000 | 5,000,000 | 5,000,000 | $ 5,000,000 | 0 | 0 | $ 0 |
Ambac UK [Member] | Consolidated Entities [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Number of consolidated Variable Interest Entities | Entity |  |  |  | 5 |  |  | 5 |
Ambac UK [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Available-for-sale Securities | 1,828,000,000 | 1,828,000,000 | 1,828,000,000 | $ 1,828,000,000 | 3,320,000,000 | 3,320,000,000 | $ 3,320,000,000 |
Restricted Cash | 1,000,000 | 1,000,000 | 1,000,000 | 1,000,000 | 1,000,000 | 1,000,000 | 1,000,000 |
Assets | 3,896,000,000 | 3,896,000,000 | 3,896,000,000 | 3,896,000,000 | 6,077,000,000 | 6,077,000,000 | 6,077,000,000 |
Liabilities | 3,836,000,000 | 3,836,000,000 | 3,836,000,000 | 3,836,000,000 | 5,996,000,000 | 5,996,000,000 | 5,996,000,000 |
Long-term Debt, Fair Value | 2,788,000,000 | 2,788,000,000 | 2,788,000,000 | 2,788,000,000 | 4,056,000,000 | 4,056,000,000 | 4,056,000,000 |
Long-term debt | 2,788,000,000 | 2,788,000,000 | 2,788,000,000 | 2,788,000,000 | 4,056,000,000 | 4,056,000,000 | 4,056,000,000 |
Financing Receivable, after Allowance for Credit Loss | 1,829,000,000 | 1,829,000,000 | 1,829,000,000 | 1,829,000,000 | 2,718,000,000 | 2,718,000,000 | 2,718,000,000 |
Derivative assets | 239,000,000 | 239,000,000 | 239,000,000 | 239,000,000 | 38,000,000 | 38,000,000 | 38,000,000 |
Other assets | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Long-term Debt, at par less amortized discount | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Derivative liabilities | 1,048,000,000 | 1,048,000,000 | 1,048,000,000 | 1,048,000,000 | 1,940,000,000 | 1,940,000,000 | 1,940,000,000 |
Other liabilities | 0 | 0 | 0 | $ 0 | 0 | 0 | $ 0 |
Ambac Assurance [Member] | Consolidated Entities [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Number of consolidated Variable Interest Entities | Entity |  |  |  | 4 |  |  | 1 |
Ambac Assurance [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Available-for-sale Securities | 139,000,000 | 139,000,000 | 139,000,000 | $ 139,000,000 | 136,000,000 | 136,000,000 | $ 136,000,000 |
Restricted Cash | 16,000,000 | 16,000,000 | 16,000,000 | 16,000,000 | 1,000,000 | 1,000,000 | 1,000,000 |
Assets | 157,000,000 | 157,000,000 | 157,000,000 | 157,000,000 | 139,000,000 | 139,000,000 | 139,000,000 |
Liabilities | 324,000,000 | 324,000,000 | 324,000,000 | 324,000,000 | 160,000,000 | 160,000,000 | 160,000,000 |
Long-term Debt, Fair Value | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Long-term debt | 319,000,000 | 319,000,000 | 319,000,000 | 319,000,000 | 160,000,000 | 160,000,000 | 160,000,000 |
Financing Receivable, after Allowance for Credit Loss | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Derivative assets | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Other assets | 2,000,000 | 2,000,000 | 2,000,000 | 2,000,000 | 2,000,000 | 2,000,000 | 2,000,000 |
Long-term Debt, at par less amortized discount | 319,000,000 | 319,000,000 | 319,000,000 | 319,000,000 | 160,000,000 | 160,000,000 | 160,000,000 |
Derivative liabilities | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Other liabilities | 5,000,000 | 5,000,000 | 5,000,000 | 5,000,000 | 0 | 0 | 0 |
Ambac Assurance Corporation [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Long-term debt | $ 639,000,000 | 639,000,000 | 639,000,000 | 639,000,000 | 2,230,000,000 | 2,230,000,000 | 2,230,000,000 |
Ambac Assurance Corporation [Member] | 5.1% Junior Surplus Notes, General Account Due 2020 [Member] | Corolla Notes |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Note Holders | 1 |  |  |  |  |  |  |
Corporate Debt Securities [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Available-for-sale Securities | $ 1,828,000,000 | 1,828,000,000 | 1,828,000,000 | 1,828,000,000 | 3,320,000,000 | 3,320,000,000 | 3,320,000,000 |
Corporate Debt Securities [Member] | Ambac UK [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Available-for-sale Securities | 1,828,000,000 | 1,828,000,000 | 1,828,000,000 | 1,828,000,000 | 3,320,000,000 | 3,320,000,000 | 3,320,000,000 |
Corporate Debt Securities [Member] | Ambac Assurance [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Available-for-sale Securities | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Municipal Bonds [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1,000,000 | 1,000,000 | 1,000,000 | 1,000,000 | 29,000,000 | 29,000,000 | 29,000,000 |
Available-for-sale Securities | 96,000,000 | 96,000,000 | 96,000,000 | 96,000,000 | 136,000,000 | 136,000,000 | 136,000,000 |
Municipal Bonds [Member] | Ambac UK [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Available-for-sale Securities | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Municipal Bonds [Member] | Ambac Assurance [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |  |  |  |
Available-for-sale Securities | $ 96,000,000 | $ 96,000,000 | $ 96,000,000 | $ 96,000,000 | $ 136,000,000 | $ 136,000,000 | $ 136,000,000 |

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