Document and Entity Information - $ / shares
6 Months Ended
Jun. 30, 2019
Aug. 05, 2019
Dec. 31, 2018
Apr. 30, 2013
Entity Information [Line Items]        
Document Type 10-Q      
Document Quarterly Report true      
Document Period End Date Jun. 30, 2019      
Entity Ex Transition Period false      
Entity File Number 1-10777      
Entity Registrant Name AMBAC FINANCIAL GROUP INC      
Entity Incorporation, State or Country Code DE      
Entity Tax Identification Number 13-3621676      
Entity Address, Address Line One One State Street Plaza      
Entity Address, City or Town New York      
Entity Address, State or Province NY      
Entity Address, Postal Zip Code 10004      
City Area Code (212)      
Local Phone Number 658-7470      
Title of 12(b) Security Common stock par value $0.01 per share      
Trading Symbol AMBC      
Security Exchange Name NASDAQ      
Entity Current Reporting Status Yes      
Entity Interactive Data Current Yes      
Entity Filer Category Large Accelerated Filer      
Entity Small Business false      
Entity Emerging Growth Company false      
Entity Shell Company false      
Entity Bankruptcy Proceedings, Reporting Current true      
Entity Common Stock, Shares Outstanding   45,551,260    
Common Stock, Par or Stated Value Per Share $ 0.01   $ 0.01 $ 0.01
Amendment Flag false      
Document Fiscal Year Focus 2019      
Document Fiscal Period Focus Q2      
Entity Central Index Key 0000874501      
Current Fiscal Year End Date --12-31