Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Capital loss carryforwards, valuation allowance	$ 183
Unrecognized tax benefits	55	$ 57	$ 53
Unrecognized tax benefits that would impact effective tax rate if recognized	55
Federal
Income Taxes [Line Items]
NOL carryforwards	9,900
Tax effected amount of NOLs	2,100
Tax credits	40
Deferred tax asset, portion to be utilized against deferred tax liabilities	6,200
Deferred tax asset, portion to be utilized against future taxable income	1,300
Federal | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	9,900
Tax effected amount of NOLs	2,100
NOLs without an expiration date	$ 8,400
Federal | Minimum
Income Taxes [Line Items]
Tax credit expiration period	1 year
Federal | Maximum
Income Taxes [Line Items]
Tax credit expiration period	18 years
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	27
State | United Airlines, Inc.
Income Taxes [Line Items]
NOL carryforwards	3,300
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	5 years
State | Maximum
Income Taxes [Line Items]
Tax credit expiration period	11 years
State | Maximum | United Airlines, Inc.
Income Taxes [Line Items]
NOL expiration period	20 years