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Document and Entity Information
 3 Months Ended
Mar. 31, 2013
May 09, 2013
Document Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2013  
Document Fiscal Year Focus 2013  
Document Fiscal Period Focus Q1  
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 Smaller Reporting Company  
Entity Common Stock, Shares Outstanding   45,000,000