Cover - USD ($)	12 Months Ended
	Dec. 31, 2025	Mar. 20, 2026	Jun. 30, 2025
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2025
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-43014
Entity Registrant Name	Andersen Group Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	33-4630773
Entity Address, Address Line One	333 Bush Street
Entity Address, Address Line Two	Suite 1700
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94104
City Area Code	415
Local Phone Number	764-2700
Title of 12(b) Security	Class A common stock, $0.0001 par value
Trading Symbol	ANDG
Security Exchange Name	NYSE
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	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 0
Documents Incorporated by Reference	Portions of the Registrant's definitive proxy statement, or the 2026 Proxy Statement, relating to its annual meeting of stockholders to be held in 2026, or the 2026 Annual Meeting, to be filed with the Securities and Exchange Commission, or the SEC, within 120 days after the end of the fiscal year to which this Annual Report on Form 10-K relates, are incorporated herein by reference where indicated. Except with respect to information specifically incorporated by reference in this Annual Report on Form 10-K, such proxy statement is not deemed to be a part hereof.
Entity Central Index Key	0002065708
Amendment Flag	false
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2025
Common Class A
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		12,650,000
Common Class B
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		98,826,563