Special Purpose Entities, Including Variable Interest Entities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Variable Interest Entities [Line Items]
Fair value of special purpose entities	10,036	$ 12,036
Consolidated VIE assets	15,506,746	15,126,110
Consolidated VIE liabilities	15,473,572	15,085,685
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
Number of transactions outstanding with special purpose entities	3
Total principal amount of debt outstanding	457,960	$ 457,960
Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number of consolidated Variable Interest Entities	14	15

The total principal amount of outstanding debt issued by Ambac's sponsored medium term note special purpose entities.

No definition available.

Name:	ambc_FaceAmountOfDebtOutstandingIssuedBySponsoredSpecialPurposeEntities
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of consolidated variable interest entities.

+ References

No definition available.

+ Details

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Namespace Prefix:	ambc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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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Namespace Prefix:	ambc_
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Balance Type:	na
Period Type:	instant

- Definition

The number of asset transfer transactions executed with Ambac's sponsored medium term note special purpose entities since the inception of those entities.

+ References

No definition available.

+ Details

Name:	ambc_NumberOfTransactionsWithSponsoredSpecialPurposeEntitiesInceptionToDate
Namespace Prefix:	ambc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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

Name:	ambc_WeightedAverageLifeOfAssetsHeldBySponsoredSpecialPurposeEntities
Namespace Prefix:	ambc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- 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

Name:	ambc_WeightedAverageRatingOfAssetsHeldBySponsoredSpecialPurposeEntities
Namespace Prefix:	ambc_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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