Income Taxes - Temporary Differences and Carryforwards Giving Rise to Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred income tax asset (liability):
Federal and state net operating loss ("NOL") carryforwards	$ 2,229	$ 2,476
Deferred revenue	2,349	1,409
Employee benefits, including pension, postretirement and medical	986	1,103
Operating lease liabilities	1,272	1,247
Other financing liabilities	327	260
Other	535	362
Less: Valuation allowance	(210)	(247)
Total deferred tax assets	7,488	6,610
Depreciation	(5,122)	(4,789)
Operating lease right-of-use asset	(1,051)	(1,028)
Intangibles	(656)	(662)
Total deferred tax liabilities	(6,829)	(6,479)
Net deferred tax asset	659	131
United Airlines, Inc.
Deferred income tax asset (liability):
Federal and state net operating loss ("NOL") carryforwards	2,201	2,448
Deferred revenue	2,349	1,409
Employee benefits, including pension, postretirement and medical	986	1,103
Operating lease liabilities	1,272	1,247
Other financing liabilities	327	260
Other	535	362
Less: Valuation allowance	(210)	(247)
Total deferred tax assets	7,460	6,582
Depreciation	(5,122)	(4,789)
Operating lease right-of-use asset	(1,051)	(1,028)
Intangibles	(656)	(662)
Total deferred tax liabilities	(6,829)	(6,479)
Net deferred tax asset	$ 631	$ 103