Junior Surplus Notes issued by the Segregated Account of Ambac Assurance to Ambac upon Ambac's emergence from bankruptcy. These Junior Surplus notes will be includable in surplus for statutory accounting purposes as prescribed or permitted by state laws and regulations.

No definition available.

Schedule II - Additional Information (Detail) (USD $)	12 Months Ended		1 Months Ended
Schedule II - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Apr. 30, 2013	May 01, 2013
Condensed Financial Statements, Captions [Line Items]
Date of incorporation	Apr. 29, 1991
Capital stock, shares authorized			150,000,000ambc_CapitalStockAuthorized
Common stock, shares authorized	130,000,000us-gaap_CommonStockSharesAuthorized	130,000,000us-gaap_CommonStockSharesAuthorized	130,000,000us-gaap_CommonStockSharesAuthorized
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000us-gaap_PreferredStockSharesAuthorized	20,000,000us-gaap_PreferredStockSharesAuthorized	20,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, par value	$ 0.01	$ 0.01	$ 0.01
Common stock, shares issued	45,005,932us-gaap_CommonStockSharesIssued	45,003,461us-gaap_CommonStockSharesIssued	45,000,000us-gaap_CommonStockSharesIssued
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			5,047,138
Warrants issued exercise price			$ 16.67
Warrant Exercised From Inception Shares	7,261
Warrant exercised	949ambc_WarrantExercisedDuringPeriodShares	6,312ambc_WarrantExercisedDuringPeriodShares
Amount transferred to escrow account			$ 30,000,000ambc_MediationAgreementCashGrant
Junior surplus note of Ambac Assurance Segregated Account				350,000,000ambc_Ambc_JuniorSurplusNotesIssued
Junior Surplus Note Fair Value on Issuance	167,020,000
Percentage of voting rights, common stock	10.00%ambc_CommonStockVotingRestrictions	10.00%ambc_CommonStockVotingRestrictions
Common Stock Voting Restriction Less One Vote	10.00%
Holder's ownership	5.00%ambc_CommonStockTransferRestrictions
Change in holder's ownership	5.00%
Voting shares of the emerging entity			50.00%
Stock Issued From Inception From Exercise Of Warrants	3,473
Par Value of Owner Trust Certificate	74,794,000ambc_ParValueofOwnerTrustCertificate
Par Value of Private Placement	299,175,000ambc_ParValueofPrivatePlacement
Private Placement Par Value Proceeds	80.00%ambc_PrivatePlacementParValueProceeds
Private Placement Maturity Date	Aug. 28, 2039
Interest Rate on Private Placement Obligations	5.10%
Ambac Financial Group, Inc Parent Company Only [Member]
Condensed Financial Statements, Captions [Line Items]
Common stock, shares authorized	130,000,000	130,000,000
Common stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	45,005,932	45,003,461
Ambac Assurance [Member]
Condensed Financial Statements, Captions [Line Items]
Reimbursement of operating expenses			5,000,000
Ambac Assurance [Member] \| 2017 [Member]
Condensed Financial Statements, Captions [Line Items]
Maximum Reimbursement Of Operating Expenses after 2017			$ 4,000,000