Document and Entity Information - shares
6 Months Ended
Jun. 30, 2017
Aug. 07, 2017
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2017  
Entity Well-known Seasoned Issuer Yes  
Entity Current Reporting Status Yes  
Entity Voluntary Filers No  
Document Fiscal Year Focus 2017  
Document Fiscal Period Focus Q2  
Trading Symbol AMBC  
Entity Registrant Name AMBAC FINANCIAL GROUP INC  
Entity Central Index Key 0000874501  
Current Fiscal Year End Date --03-31  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   45,251,166