Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Feb. 28, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity File Number	1-07265
Entity Registrant Name	AMBASE CORPORATION
Entity Central Index Key	0000020639
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	95-2962743
Entity Address, Address Line One	7857 West Sample Road, Suite 134
Entity Address, City or Town	Coral Springs
Entity Address, State or Province	FL
Entity Address, Postal Zip Code	33065
City Area Code	201
Local Phone Number	265-0169
Title of 12(g) Security	Common Stock ($0.01 par value)
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		40,737,751
Entity Public Float			$ 7
Auditor Firm ID	688
Auditor Name	Marcum LLP
Auditor Location	Hartford, Connecticut