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Outstanding Exposure - Narrative (Details) $ in Millions |  | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 26, 2023 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2023 USD ($) exposure | Aug. 31, 2023 USD ($) | Jun. 23, 2023 USD ($) | Dec. 31, 2022 USD ($)
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Loss Mitigation Securities |  | $ 1,200 | $ 1,200 |  |  | $ 1,300
Net Par Outstanding |  | 249,153 | 249,153 | $ 108 |  | 233,258
Fixed-maturity securities, available-for-sale, at fair value, net of allowance for credit loss |  | 6,307 | $ 6,307 |  |  | 7,119
Insured exposure in payment default, number | exposure |  |  | 1 |  |  |
Maximum exposure, undiscounted |  | 1,600 | $ 1,600 |  |  |
PREPA |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Plaintiff debt capacity |  |  |  |  | $ 2,500 |
Settling creditors |  |  |  |  | 1,400 |
Bondholders and general unsecured creditors |  |  |  |  | $ 1,100 |
Claim received as restructuring bonds, percent |  |  |  |  | 12.50% |
PREPA | 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, value | $ 8,500 |  |  |  |  |
Puerto Rico |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Net Par Outstanding |  | 1,105 | 1,105 |  |  | 1,361
Puerto Rico | Puerto Rico Highways and Transportation Authority |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Net Par Outstanding |  | 372 | 372 |  |  |
Proceeds from bonds called |  | 154 |  |  |  |
Puerto Rico | Other Puerto Rico Exposures |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Net Par Outstanding |  | 109 | 109 |  |  | 132
Puerto Rico | Other Puerto Rico Exposures | MFA |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Net Par Outstanding |  | 108 | 108 |  |  | 131
Puerto Rico Trusts | Variable Interest Entity, Primary Beneficiary | Financial Guaranty Variable Interest Entities |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Fixed-maturity securities, available-for-sale, at fair value, net of allowance for credit loss |  |  |  | $ 73 |  | 204
Public finance |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Net Par Outstanding |  | 239,296 | 239,296 |  |  | 224,099
Public finance | Commitment to Provide Guarantees |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Outstanding commitments to provide guaranties |  | 193 | 193 |  |  |
Structured finance |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Net Par Outstanding |  | 9,857 | 9,857 |  |  | 9,159
Structured finance | Commitment to Provide Guarantees |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Outstanding commitments to provide guaranties |  | 1,700 | $ 1,700 |  |  |
BIG |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Maximum period of liquidity claims (in years) |  |  | 1 year |  |  |
Net Par Outstanding |  | 5,437 | $ 5,437 |  |  | 5,892
BIG | Puerto Rico |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Net Par Outstanding |  | 1,100 | 1,100 |  |  | 1,400
BIG | Public finance |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Net Par Outstanding |  | 4,402 | 4,402 |  |  | 4,777
BIG | Structured finance |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Net Par Outstanding |  | 1,035 | 1,035 |  |  | 1,115
BIG | Aircraft residual value insurance policies |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Specialty business, gross par |  | 144 | 144 |  |  | 144
Specialty business, net par |  | $ 84 | $ 84 |  |  | $ 84
Minimum |  |  |  |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |  |  |  |
Probability of paying more claims than being reimbursed (as a percent) |  | 50.00% | 50.00% |  |  |

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