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Fair Value Measurements - Information about Valuation Inputs for Variable Interest Entity Assets and Liabilities Classified as Level 3 (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Estimated Future Premium Payments Weighted Average Discounted Rate | 3.00% | 2.20% |
Asset-backed Securities [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Inputs Coupon Rate | 5.98% | 5.97% |
Fair Value Inputs Maturity | 13 years 5 months 15 days | 14 years 1 month 20 days |
Fair Value Inputs Yield | 12.60% | 10.20% |
Variable Interest Entity [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held |  |  | $ 281
Estimated Future Premium Payments Weighted Average Discounted Rate | 6.80% | 3.00% |
Estimated Future Premium Payments Minimum Discounted Rate | 5.80% | 2.20% |
Estimated Future Premium Payments Maximum Discounted Rate | 8.50% | 4.10% |

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- Definition Estimated Future Premium Payments Maximum Discounted Rate + References No definition available. + Details
Name: | ambc_EstimatedFuturePremiumPaymentsMaximumDiscountedRate
Namespace Prefix: | ambc_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Estimated Future Premium Payments Minimum Discounted Rate + References No definition available. + Details
Name: | ambc_EstimatedFuturePremiumPaymentsMinimumDiscountedRate
Namespace Prefix: | ambc_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Weighted average discounted rate of estimated future premium payments to be paid by the VIEs. + References No definition available. + Details
Name: | ambc_EstimatedFuturePremiumPaymentsWeightedAverageDiscountedRate
Namespace Prefix: | ambc_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition The amount of gains or losses included in earnings attributable to unrealized gains or losses on financial instruments measured on a recurring basis using unobservable inputs that are still held at the reporting date. + References No definition available. + Details
Name: | ambc_FairValueAssetOrLiabilityMeasuredOnRecurringBasisChangeInUnrealizedGainsLossesStillHeld
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Fair value inputs coupon rate. + References No definition available. + Details
Name: | ambc_FairValueInputsCouponRate
Namespace Prefix: | ambc_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Fair value inputs maturity. + References No definition available. + Details
Name: | ambc_FairValueInputsMaturity
Namespace Prefix: | ambc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Fair value inputs yield. + References No definition available. + Details
Name: | ambc_FairValueInputsYield
Namespace Prefix: | ambc_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FairValueOptionQuantitativeDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |