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v3.22.0.1

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, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Estimated Future Premium Payments Weighted Average Discounted Rate | 2.20% | 2.20% |
Asset-backed Securities [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Inputs Coupon Rate | 5.97% | 5.97% |
Fair Value Inputs Maturity | 14 years 1 month 20 days | 14 years 9 months 29 days |
Fair Value Inputs Yield | 10.20% | 10.50% |
Fair Value, Inputs, Level 3 [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies |  | $ 0 | $ 627
Fair Value, Inputs, Level 3 [Member] | Investments [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies |  | 0 | 0
Fair Value, Inputs, Level 3 [Member] | Other Assets [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies |  | 0 | 0
Fair Value, Inputs, Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies |  | 0 |
Loan Origination Commitments [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies |  | 0 |
Investment Contracts [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies |  | $ 0 |
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 |  |  | 353
Estimated Future Premium Payments Weighted Average Discounted Rate | 3.00% | 2.40% |
Estimated Future Premium Payments Minimum Discounted Rate | 2.20% |  |
Estimated Future Premium Payments Maximum Discounted Rate | 4.10% |  |
Variable Interest Entity [Member] | Loan Origination Commitments [Member] | Fair Value, Inputs, Level 3 [Member] | Loans Receivable [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies |  |  | 851
Variable Interest Entity [Member] | Long-term Debt [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies |  |  | (223)
Variable Interest Entity [Member] | Investment Contracts [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member] |  |  |
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |  |
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Deconsolidation Of Vies |  |  | $ 0

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

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- Definition Fair value inputs maturity. + References No definition available. + Details
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- Definition Fair value inputs yield. + References No definition available. + Details
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Balance Type: | na
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- Definition Fair value of financial instruments measured on a recurring basis using unobservable inputs removed as a result of the deconsolidation of variable interest entities. + References No definition available. + Details
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Balance Type: | debit
Period Type: | duration

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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
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