Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 20, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-06033
Entity Registrant Name	United Airlines Holdings, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-2675207
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 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 Common Stock, Shares Outstanding		323,578,254
Document Fiscal Period Focus	Q1
Amendment Flag	false
Document Fiscal Year Focus	2021
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0000100517
Common Stock
Entity Information [Line Items]
Title of 12(b) Security	Common Stock,
Trading Symbol	UAL
Security Exchange Name	NASDAQ
Preferred Stock Purchase Rights
Entity Information [Line Items]
Title of 12(b) Security	Preferred Stock Purchase Rights
No Trading Symbol Flag	true
Security Exchange Name	NASDAQ
United Airlines, Inc.
Entity Information [Line Items]
Entity File Number	001-10323
Entity Registrant Name	United Airlines, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	74-2099724
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,000
Entity Central Index Key	0000319687