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Special Purpose Entities, Including Variable Interest Entities - Additional Information (Detail) (USD $) | 8 Months Ended | 12 Months Ended | 4 Months Ended | 12 Months Ended | 1 Months Ended
--- | --- | --- | --- | --- | ---
Dec. 31, 2013 | Dec. 31, 2014 | Apr. 30, 2013 | Dec. 31, 2012 | Apr. 30, 2013
Variable Interest Entities [Line Items] |  |  |  |  |
Fair value of special purpose entities | $ 13,384,000 us-gaap_EquityMethodInvestmentsFairValueDisclosure | $ 12,036,000 us-gaap_EquityMethodInvestmentsFairValueDisclosure |  |  |
Consolidated VIE assets | 15,988,697,000 us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets | 15,126,110,000 us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets |  |  |
Consolidated VIE liabilities | 15,872,770,000 us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities | 15,085,685,000 us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities |  |  |
Variable interest entities deconsolidation gain (loss) | 15,273,000 ambc_Ambc_variableinterestentitiesdeconsolidationgainloss |  |  |  |
Successor [Member] |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |
Claims on insurance policies issued to these entities | 2,747,000 ambc_AmountsRecoveredOnPreviouslyPaidClaimsRelatedToSponsoredSpecialPurposeEntities / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 988,000 ambc_AmountsRecoveredOnPreviouslyPaidClaimsRelatedToSponsoredSpecialPurposeEntities / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember |  |  |
Predecessor [Member] |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |
Claims on insurance policies issued to these entities |  |  | 1,455,000 ambc_AmountsRecoveredOnPreviouslyPaidClaimsRelatedToSponsoredSpecialPurposeEntities / us-gaap_StatementScenarioAxis = us-gaap_PredecessorMember | 14,691,000 ambc_AmountsRecoveredOnPreviouslyPaidClaimsRelatedToSponsoredSpecialPurposeEntities / us-gaap_StatementScenarioAxis = us-gaap_PredecessorMember |
Asset-Backed Securities and Utility Obligations [Member] |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |
Weighted average life |  | 6 years 9 months 12 days |  |  |
Average rating of assets held by sponsored special purpose entities |  | BBB |  |  |
Sponsored Variable Interest Entities [Member] |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |
Number of individual transactions with special purpose entities |  | 15 ambc_NumberOfTransactionsWithSponsoredSpecialPurposeEntitiesInceptionToDate / us-gaap_GuaranteeObligationsByNatureAxis = ambc_SponsoredVariableInterestEntitiesMember |  |  |
Number of transactions outstanding with special purpose entities |  | 3 ambc_NumberOfTransactionsOutstandingWithSponsoredSpecialPurposeEntities / us-gaap_GuaranteeObligationsByNatureAxis = ambc_SponsoredVariableInterestEntitiesMember |  |  |
Total principal amount of debt outstanding | 461,355,000 ambc_FaceAmountOfDebtOutstandingIssuedBySponsoredSpecialPurposeEntities / us-gaap_GuaranteeObligationsByNatureAxis = ambc_SponsoredVariableInterestEntitiesMember | 457,960,000 ambc_FaceAmountOfDebtOutstandingIssuedBySponsoredSpecialPurposeEntities / us-gaap_GuaranteeObligationsByNatureAxis = ambc_SponsoredVariableInterestEntitiesMember |  |  |
Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |
Secured Debt | 0 us-gaap_SecuredDebt / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember | 0 us-gaap_SecuredDebt / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember |  |  |
Variable Interest Entities [Member] | Successor [Member] |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |
Amortization Of Variable Interest Entity Intangible Assets | 5,015,000 ambc_AmortizationOfVariableInterestEntityIntangibleAssets / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember |  |  |  |
Asset Impairment Charges | 76,140 us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember |  |  |  |
Variable Interest Entities [Member] | Predecessor [Member] |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |
Variable Interest Entity, Initial Consolidation, Gain (Loss) |  |  |  |  | 385,291,000 us-gaap_VariableInterestEntityInitialConsolidationGainOrLoss / us-gaap_StatementScenarioAxis = us-gaap_PredecessorMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Fair Value Intangible Assets Initially Recorded Upon Consolidation Of Variable Interest Entity |  |  | $ 164,520,000 ambc_FairValueIntangibleAssetsInitiallyRecordedUponConsolidationOfVariableInterestEntity / us-gaap_StatementScenarioAxis = us-gaap_PredecessorMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember |  | $ 164,520,000 ambc_FairValueIntangibleAssetsInitiallyRecordedUponConsolidationOfVariableInterestEntity / us-gaap_StatementScenarioAxis = us-gaap_PredecessorMember / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life |  |  |  |  | 16 years 0 months 0 days
Consolidated Entities [Member] |  |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |  |
Number of consolidated Variable Interest Entities | 18 ambc_NumberOfConsolidatedVariableInterestEntities / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember | 15 ambc_NumberOfConsolidatedVariableInterestEntities / dei_LegalEntityAxis = us-gaap_ConsolidatedEntitiesMember |  |  |

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- Definition The expense charged against earnings to allocate the fair value of consolidated VIE intangible assets to the periods expected to benefit from such assets. + References No definition available. + Details
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- Definition Amounts recovered in respect of previously paid claims on insurance policies issued to Ambac's sponsored special purpose entities. + References No definition available. + Details
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- Definition The total principal amount of outstanding debt issued by Ambac's sponsored medium term note special purpose entities. + References No definition available. + Details
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- Definition Amount of intangible assets at fair value recorded upon the initial consolidation of a variable interest entity when consolidation occurred during the period(s) reported. + References No definition available. + Details
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- Definition Number of consolidated variable interest entities. + References No definition available. + Details
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- Definition The number of asset transfer transactions executed with Ambac's sponsored medium term note special purpose entities that are still outstanding at the reporting date. + References No definition available. + Details
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- Definition The weighted average remaining life of assets held by Ambac's sponsored medium term note special purpose entities at the reporting date. + References No definition available. + Details
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- Definition The weighted average credit rating of assets held by Ambac's sponsored medium term note special purpose entities at the reporting date. + References No definition available. + Details
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- Definition Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16265-109275 + Details
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- Definition Fair value portion of investments accounted under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35740979&loc=d3e32014-111567 + Details
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- Definition Fair value portion of assets, excluding financial assets, that lack physical substance, having a limited useful life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19190-110258 + Details
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- Definition Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685 + Details
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- Definition The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685 + Details
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- Definition The gain (loss) recognized on initial consolidation of a variable interest entity (VIE) when the VIE is not a business (as defined). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685 + Details
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