Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 24, 2020	Dec. 31, 2018	Jun. 30, 2018	Apr. 30, 2013
Entity Information [Line Items]
Entity File Number	1-10777
Document Quarterly Report	true
Document Transition Report	false
City Area Code	(212)
Entity Incorporation, State or Country Code	DE
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
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		45,577,874
Entity Public Float				$ 767,503,767
Common Stock, Par or Stated Value Per Share	$ 0.01		$ 0.01		$ 0.01
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
Local Phone Number	658-7470
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
Warrant [Member]
Entity Information [Line Items]
Title of 12(b) Security	Warrants
Trading Symbol	AMBC WS
Security Exchange Name	NYSE