XML 21 R1.htm IDEA: XBRL DOCUMENT v3.10.0.1
Document and Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2018
Feb. 25, 2019
Jun. 30, 2018
Dec. 31, 2017
Apr. 30, 2013
Entity Information [Line Items]          
Document Type 10-K        
Amendment Flag false        
Document Period End Date Dec. 31, 2018        
Entity Well-known Seasoned Issuer Yes        
Entity Current Reporting Status Yes        
Entity Voluntary Filers No        
Document Fiscal Year Focus 2018        
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 Emerging Growth Company false        
Entity Small Business false        
Entity Filer Category Large Accelerated Filer        
Entity Shell Company false        
Entity Common Stock, Shares Outstanding   45,341,834      
Entity Public Float     $ 899,844,448    
Common Stock, Par or Stated Value Per Share $ 0.01     $ 0.01 $ 0.01