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Outstanding Exposure - Additional Information (Details) $ in Millions |  | 3 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 26, 2023 USD ($) | Mar. 31, 2024 USD ($) Category | Dec. 31, 2023 USD ($) | Jun. 23, 2023 USD ($)
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Number of surveillance categories | Category |  | 3 |  |
Loss Mitigation Securities |  | $ 1,200 | $ 1,200 |
Net par outstanding |  | 248,144 | 249,153 |
Estimated Fair Value |  | 6,091 | 6,307 |
Fixed-maturity securities, trading |  | 272 | 318 |
Guarantor, maximum exposure |  | 1,500 |  |
Puerto Rico Electric Power Authority |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Plaintiff debt capacity |  |  |  | $ 2,500
Plaintiff debt capacity allocated to settling creditors |  |  |  | 1,400
Plaintiff debt capacity allocated to bondholders and general unsecured creditors |  |  |  | $ 1,100
Claim received as restructuring bonds, percent |  |  |  | 12.50%
Puerto Rico Electric Power Authority | Guarantee Obligations |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Damages sought, estimate | $ 2,400 |  |  |
Calculated collection period | 100 years |  |  |
Calculated discount rate | 7.00% |  |  |
Calculated discounted cash flows | $ 3,000 |  |  |
Additional calculated discount rate | 20.00% |  |  |
Damages sought | $ 8,500 |  |  |
Puerto Rico |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Net par outstanding |  | 961 | 1,105 |
Puerto Rico | Puerto Rico Defaulted Exposures Subject to a Plan Support Agreement | Puerto Rico Electric Power Authority |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Net par outstanding |  | 624 | 624 |
Public finance |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Net par outstanding |  | 238,132 | 239,296 |
Structured finance |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Net par outstanding |  | 10,012 | 9,857 |
Aircraft residual value insurance (RVI) |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Residual value insurance policies exposure downgraded |  | 355 | 355 |
Net Exposure |  | 200 | 200 |
Commitment to Provide Guarantees | Public finance |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Outstanding commitments to provide guaranties |  | 829 |  |
Potential future commitment |  |  | 353 |
Commitment to Provide Guarantees | Structured finance |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Outstanding commitments to provide guaranties |  | $ 1,800 |  |
Potential future commitment |  |  | 50 |
BIG |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Maximum period of liquidity claims (in years) |  | 1 year |  |
Net par outstanding |  | $ 5,193 | 5,437 |
BIG | Public finance |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Net par outstanding |  | 4,224 | 4,402 |
BIG | Structured finance |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Net par outstanding |  | 969 | 1,035 |
BIG | Aircraft residual value insurance (RVI) |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Residual value insurance policies exposure downgraded |  | 144 | 144 |
Net Exposure |  | $ 84 | $ 84 |
Minimum |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |
Probability of paying more claims than being reimbursed (as a percent) |  | 50.00% |  |

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