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Financial Guarantees in Force - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013
Guarantor Obligations [Line Items] |  |
Gross par amount of financial guarantees outstanding | 159,688,000 ambc_FinancialGuaranteeGrossOutstandingPrincipal | $ 197,691,000 ambc_FinancialGuaranteeGrossOutstandingPrincipal
Net par amount of financial guarantees | 144,734,000 us-gaap_ParticipatingPoliciesAmountInForce | 179,092,000 us-gaap_ParticipatingPoliciesAmountInForce
Gross financial guarantees in force | 253,383,000 ambc_FinancialGuaranteeGrossOutstandingPrincipalAndInterest | 312,710,000 ambc_FinancialGuaranteeGrossOutstandingPrincipalAndInterest
Net financial guarantees in force | 228,890,000 ambc_NetFinancialGuaranteePrincipalAndInterestInForce | $ 282,210,000 ambc_NetFinancialGuaranteePrincipalAndInterestInForce
Highest single insured risk of aggregate net par amount guaranteed | 1.40%ambc_PercentageOfHighestSingleInsuredRiskOfAggregateNetParAmountGuaranteed |
California [Member] |  |
Guarantor Obligations [Line Items] |  |
Aggregate net par amounts in force | 14.30%ambc_PercentageOfAggregateGuaranteedInsuredRiskByNetPar / us-gaap_StatementGeographicalAxis = stpr_CA |
New York [Member] |  |
Guarantor Obligations [Line Items] |  |
Aggregate net par amounts in force | 6.40%ambc_PercentageOfAggregateGuaranteedInsuredRiskByNetPar / us-gaap_StatementGeographicalAxis = stpr_NY |
No other state [Member] | Maximum [Member] |  |
Guarantor Obligations [Line Items] |  |
Aggregate net par amounts in force | 5.00%ambc_PercentageOfAggregateGuaranteedInsuredRiskByNetPar / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_StatementGeographicalAxis = ambc_UnitedStatesNonCaliforniaAndNonNewYorkMember |

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- Definition Financial guarantee insurance gross outstanding principal. + References No definition available. + Details
Name: | ambc_FinancialGuaranteeGrossOutstandingPrincipal
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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- Details
Name: | us-gaap_GuaranteeObligationsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount as of the balance sheet date of the participating business in force. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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
Name: | us-gaap_ParticipatingPoliciesAmountInForce
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_StatementGeographicalAxis=ambc_UnitedStatesNonCaliforniaAndNonNewYorkMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementGeographicalAxis=stpr_CA
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementGeographicalAxis=stpr_NY
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |