Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Taxes [Line Items]
Capital loss carryforwards, valuation allowance	$ 175
Unrecognized tax benefits	58	$ 55	$ 57
Unrecognized tax benefits that would impact effective tax rate if recognized	58
Federal
Income Taxes [Line Items]
NOL carryforwards	13,200
Tax effected amount of NOLs	2,800
Tax credits	44
Deferred tax asset, portion to be utilized against deferred tax liabilities	6,700
Deferred tax asset, portion to be utilized against future taxable income	800
Federal | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	13,200
Tax effected amount of NOLs	2,800
NOLs without an expiration date	$ 11,600
Federal | Minimum
Income Taxes [Line Items]
Tax credit expiration period	1 year
Federal | Maximum
Income Taxes [Line Items]
Tax credit expiration period	20 years
Federal | 2026 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	$ 100
Federal | 2028 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	500
Federal | 2029 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	400
Federal | 2032 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	200
Federal | 2033 | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	400
State
Income Taxes [Line Items]
Tax credits	45
NOL and tax credit carryforwards, valuation allowance	24
State | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	3,900
Tax effected amount of NOLs	$ 200
State | Minimum
Income Taxes [Line Items]
Tax credit expiration period	1 year
State | Minimum | United Airlines, Inc.
Income Taxes [Line Items]
NOL expiration period	1 year
State | Maximum
Income Taxes [Line Items]
Tax credit expiration period	15 years
State | Maximum | United Airlines, Inc.
Income Taxes [Line Items]
NOL expiration period	20 years