Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Feb. 25, 2016
Jun. 30, 2015
Document And Entity Information [Abstract]        
Document Type   10-K    
Amendment Flag   false    
Document Period End Date Dec. 31, 2015      
Entity Well-known Seasoned Issuer   Yes    
Entity Current Reporting Status   Yes    
Entity Voluntary Filers   No    
Document Fiscal Year Focus   2015    
Document Fiscal Period Focus   FY    
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     45,046,996  
Entity Public Float       $ 746,545,180