Document and Entity Information - shares
9 Months Ended
Sep. 30, 2017
Nov. 03, 2017
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 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 Q3  
Trading Symbol AMBC  
Entity Registrant Name AMBAC FINANCIAL GROUP INC  
Entity Central Index Key 0000874501  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   45,251,166