Income Taxes - Temporary Differences and Carryforwards Giving Rise to Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred income tax asset (liability):
Federal and state net operating loss ("NOL") carryforwards	$ 2,644	$ 2,932
Deferred revenue	1,845	1,783
Employee benefits, including pension, postretirement and medical	695	606
Operating lease liabilities	1,134	1,118
Other financial liabilities	414	141
Interest expense carryforward	579	510
Other	575	576
Less: Valuation allowance	(179)	(199)
Total deferred tax assets	7,707	7,467
Depreciation	(6,782)	(5,844)
Operating lease right-of-use asset	(887)	(881)
Intangibles	(632)	(651)
Total deferred tax liabilities	(8,301)	(7,376)
Net deferred tax liability	(594)
Net deferred tax asset		91
United Airlines, Inc.
Deferred income tax asset (liability):
Federal and state net operating loss ("NOL") carryforwards	2,616	2,903
Deferred revenue	1,845	1,783
Employee benefits, including pension, postretirement and medical	695	606
Operating lease liabilities	1,134	1,118
Other financial liabilities	414	141
Interest expense carryforward	579	510
Other	575	576
Less: Valuation allowance	(179)	(199)
Total deferred tax assets	7,679	7,438
Depreciation	(6,782)	(5,844)
Operating lease right-of-use asset	(887)	(881)
Intangibles	(632)	(651)
Total deferred tax liabilities	(8,301)	(7,376)
Net deferred tax liability	$ (622)
Net deferred tax asset		$ 62