Background and Business Description - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2013
Background And Basis Of Presentation [Line Items]
Percentage of voting rights, common stock	10.00%
Holder's ownership	5.00%
Change in holder's ownership	5.00%
Insurance liabilities allocated to segregated account	$ 6,130,867
Percentage of permitted policy claim	25.00%
Accrued rate of interest on outstanding policy obligations	5.10%
Minimum [Member]
Background And Basis Of Presentation [Line Items]
Minimum surplus amount	100,000
Ambac Assurance [Member]
Background And Basis Of Presentation [Line Items]
Net par exposure for policies allocated to the Segregated Account	23,729,552
Issuance of secured note to segregated account	2,000,000
Secured note maturity year	2050
Interest on the secured note accrues	4.50%
Available secured notes including capitalized interest	195,831
Policyholders surplus	$ 501,672

Rate at which the secured note accrues interest.

No definition available.

Name:	ambc_AccruedInterestRatePercentage
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	ambc_BackgroundAndBasisOfPresentationLineItems
Namespace Prefix:	ambc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Change In Beneficial Ownership Percentage

+ References

No definition available.

+ Details

Name:	ambc_ChangeInBeneficialOwnershipPercentage
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Common Stock Voting Rights Percentage

+ References

No definition available.

+ Details

Name:	ambc_CommonStockVotingRightsPercentage
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the effective interest rate on deferred payment obligations of the Segregated Account of Ambac as directed by the Rehabilitator of the Segregated Account.

+ References

No definition available.

+ Details

Name:	ambc_DeferredPaymentObligationAccruedInterestRate
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of insurance liabilities allocated to the Segregated Account of Ambac Assurance from Ambac Assurance as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

Net par outstanding for policies allocated to the Segregated Account of Ambac Assurance.

+ References

No definition available.

+ Details

Name:	ambc_NetParExposureForPoliciesAllocatedToSegregatedAccount
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage of the Segregated Account of Ambac Assurance's permitted policy claims that are currently being paid in cash.

+ References

No definition available.

+ Details

Name:	ambc_PaymentAsPercentageOfPermittedPolicyClaim
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage Of Beneficial Ownership

+ References

No definition available.

+ Details

Name:	ambc_PercentageOfBeneficialOwnership
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Original issuance amount of the Secured Note issued by Ambac Assurance to the Segregated Account of Ambac Assurance in connection with the establishment of the Ambac Assurance Segregated Account.

+ References

No definition available.

+ Details

Name:	ambc_SecuredNoteIssued
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Secured note year of maturity.

+ References

No definition available.

+ Details

Name:	ambc_SecuredNoteMaturityYear
Namespace Prefix:	ambc_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Current amount outstanding, including capitalized interest, relating to a Secured Note issued by Ambac Assurance to the Segregated Account of Ambac Assurance in connection with the establishment of the Ambac Assurance Segregated Account.

+ References

No definition available.

+ Details

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

- Definition

The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.23(c))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 24

-Subparagraph c

-Article 7

+ Details

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

- Definition

Amount of statutory capital required to be maintained as of the balance sheet date under prescribed or permitted statutory accounting practices.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

+ Details

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