Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2021	Feb. 10, 2022	Jun. 30, 2021
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-06033
Entity Registrant Name	United Airlines Holdings, Inc.
Entity Address, Address Line One	233 South Wacker Drive,
Entity Address, City or Town	Chicago,
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60606
City Area Code	(872)
Local Phone Number	825-4000
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-2675207
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 16.9
Entity Common Stock, Shares Outstanding		324,626,332
Documents Incorporated by Reference	Certain information required by Items 10, 11, 12 and 13 of Part III of this Form 10-K is incorporated by reference for United Airlines Holdings, Inc. from its definitive proxy statement for its 2022 Annual Meeting of Stockholders.
Document Fiscal Period Focus	FY
Amendment Flag	false
Document Fiscal Year Focus	2021
Entity Central Index Key	0000100517
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	UAL
Security Exchange Name	NASDAQ
Preferred Stock Purchase Rights
Document Information [Line Items]
Title of 12(b) Security	Preferred Stock Purchase Rights
United Airlines, Inc.
Document Information [Line Items]
Entity File Number	001-10323
Entity Registrant Name	United Airlines, Inc.
Entity Address, Address Line One	233 South Wacker Drive,
Entity Address, City or Town	Chicago,
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60606
City Area Code	(872)
Local Phone Number	825-4000
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	74-2099724
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,000
Entity Central Index Key	0000319687