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, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Taxes [Line Items]
Income tax provision (benefit) at statutory rate	$ 208	$ (537)	$ (1,852)
State income tax provision (benefit), net of federal income tax benefit	13	(34)	(110)
Nondeductible employee meals	12	7	5
Nondeductible transportation fringe benefit	10	8	7
Valuation allowance	(10)	(38)	197
Other, net	20	1	0
Income tax expense (benefit)	253	(593)	(1,753)
Current	5	(10)	(12)
Deferred	248	(583)	(1,741)
United Airlines, Inc.
Income Taxes [Line Items]
Income tax expense (benefit)	253	(593)	(1,753)
Deferred	$ 248	$ (583)	$ (1,741)