Income Taxes - Income Tax Provision (Benefit) Differed from Amounts Computed at the Statutory Federal Income Tax Rate and Significant Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Income tax provision (benefit) at statutory rate	$ (537)	$ (1,852)	$ 822
State income tax provision (benefit), net of federal income tax benefit	(34)	(110)	50
Foreign tax rate differential	0	0	(90)
Global intangible low-taxed income	0	0	90
Nondeductible employee meals	7	5	12
Valuation allowance	(38)	197	(4)
Other, net	9	7	25
Income tax expense (benefit)	(593)	(1,753)	905
Current	(10)	(12)	23
Deferred	(583)	(1,741)	882
United Airlines, Inc.
Income Taxes [Line Items]
Income tax expense (benefit)	(593)	(1,753)	905
Deferred	$ (583)	$ (1,741)	$ 882