Document and Entity Information - $ / shares	6 Months Ended
	Jun. 30, 2020	Aug. 03, 2020	Dec. 31, 2019	Apr. 30, 2013
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
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 World Trade Center
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10007
City Area Code	(212)
Local Phone Number	658-7470
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		45,809,139
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	Q3
Entity Central Index Key	0000874501
Current Fiscal Year End Date	--12-31
Common Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Common stock par value $0.01 per share
Trading Symbol	AMBC
Security Exchange Name	NYSE
Warrants [Member]
Entity Information [Line Items]
Title of 12(b) Security	Warrants
Trading Symbol	AMBC WS
Security Exchange Name	NYSE