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Financial Guarantees in Force - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Guarantor Obligations [Line Items] |  |  |
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount | $ 10 | $ 32 | $ 64
Gross par amount of financial guarantees outstanding | 43,908 | 52,055 |
Net par amount of financial guarantees | 38,018 | 46,927 |
Gross financial guarantees in force | 69,826 | 87,543 |
Net financial guarantees in force | $ 58,245 | $ 77,972 |
Highest single insured risk of aggregate net par amount guaranteed |  | 2.70% |
California [Member] |  |  |
Guarantor Obligations [Line Items] |  |  |
Aggregate net par amounts in force | 6.70% |  |
NEW JERSEY |  |  |
Guarantor Obligations [Line Items] |  |  |
Aggregate net par amounts in force | 6.30% |  |
NEW YORK |  |  |
Guarantor Obligations [Line Items] |  |  |
Aggregate net par amounts in force | 6.10% |  |
No other state [Member] | Maximum [Member] |  |  |
Guarantor Obligations [Line Items] |  |  |
Aggregate net par amounts in force | 5.00% |  |
Public Finance [Member] |  |  |
Guarantor Obligations [Line Items] |  |  |
Net par amount of financial guarantees | $ 17,653 | $ 23,442 |
Public Finance [Member] | Housing Revenue [Member] |  |  |
Guarantor Obligations [Line Items] |  |  |
Net par amount of financial guarantees | 5,991 | 6,159 |
Military Housing [Domain] | Public Finance [Member] | Housing Revenue [Member] |  |  |
Guarantor Obligations [Line Items] |  |  |
Net par amount of financial guarantees | $ 5,654 | $ 5,759 |

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- Definition Financial guarantee insurance gross outstanding principal. + References No definition available. + Details
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Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Financial guarantee insurance gross outstanding principal and interest. + References No definition available. + Details
Name: | ambc_FinancialGuaranteeGrossOutstandingPrincipalAndInterest
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Financial guarantee insurance outstanding principal and interest, net of reinsurance. + References No definition available. + Details
Name: | ambc_NetFinancialGuaranteePrincipalAndInterestInForce
Namespace Prefix: | ambc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Percentage of related member outstanding par, net of reinsurance, as compared to the Company's total outstanding financial guarantee par, net of reinsurance. + References No definition available. + Details
Name: | ambc_PercentageOfAggregateGuaranteedInsuredRiskByNetPar
Namespace Prefix: | ambc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage of highest single insured risk of aggregate net par amount guaranteed + References No definition available. + Details
Name: | ambc_PercentageOfHighestSingleInsuredRiskOfAggregateNetParAmountGuaranteed
Namespace Prefix: | ambc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition This element represents the amount of premium revenue on financial guarantee insurance contracts recognized during the period that was accelerated for revenue recognition purposes. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291 + Details
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Balance Type: | credit
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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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of participating insurance in force. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 50 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6483535&loc=d3e16392-158451 + Details
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Namespace Prefix: | us-gaap_
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- Details
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- Details
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementGeographicalAxis=ambc_UnitedStatesNonCaliforniaAndNonNewYorkMember
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Balance Type: |
Period Type: |

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- Details
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- Details
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- Details
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- Details
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