Overview (Details) employee in Thousands					1 Months Ended	2 Months Ended	3 Months Ended									12 Months Ended
	Sep. 28, 2020 USD ($)	Jul. 02, 2020 USD ($)	Apr. 21, 2020 USD ($)	Apr. 20, 2020 USD ($)	Jul. 31, 2020 employee	Feb. 25, 2021 USD ($)	Mar. 31, 2021	Dec. 31, 2020 USD ($) employee	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) employee	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Feb. 15, 2021 USD ($)	Jan. 15, 2021 USD ($)
Unusual or Infrequent Item, or Both [Line Items]
Net income (loss)								$ (1,897,000,000)	$ (1,841,000,000)	$ (1,627,000,000)	$ (1,704,000,000)	$ 641,000,000	$ 1,024,000,000	$ 1,052,000,000	$ 292,000,000	$ (7,069,000,000)	$ 3,009,000,000	$ 2,122,000,000
Percent of capacity cut																57.00%
Rolling cancellation period																60 days
Proceeds from issuance of debt																$ 16,044,000,000	1,847,000,000	1,594,000,000
Proceeds from the issuance of common stock			$ 1,100,000,000													2,100,000,000
Payroll taxes deferred under the CARES Act																$ 199,000,000
Number of employees notified of plans for workforce reduction | employee					36
Number of employee furloughs | employee								13								13
Number of employees subject to voluntary options | employee								9								9
Total funding provided under the Payroll Support Program				$ 5,100,000,000
Funding provided through direct grants under the Payroll Support Program				3,600,000,000
Funding provided through loans under the Payroll Support Program				$ 1,500,000,000
Cash received under the Payroll Support Program																$ 5,100,000,000
Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Total funding provided under the Payroll Support Program																				$ 2,600,000,000
Funding provided through direct grants under the Payroll Support Program																				$ 1,900,000,000
Cash received under the Payroll Support Program						$ 1,300,000,000
Forecast
Unusual or Infrequent Item, or Both [Line Items]
Percent of capacity cut							51.00%
CARES Act Credit Agreement | Line of Credit
Unusual or Infrequent Item, or Both [Line Items]
Credit agreement								$ 7,500,000,000								7,500,000,000
Notes, Secured Term Loans and Aircraft Financing
Unusual or Infrequent Item, or Both [Line Items]
Proceeds from issuance of debt																$ 13,400,000,000
Unsecured Debt | PSP Note
Unusual or Infrequent Item, or Both [Line Items]
Term of debt				10 years
Unsecured Debt | PSP2 Note | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Funding provided through loans under the Payroll Support Program																			$ 753,000,000
Term of debt						10 years
Line of Credit | CARES Act Credit Agreement
Unusual or Infrequent Item, or Both [Line Items]
Proceeds from issuance of debt	$ 520,000,000
Credit agreement	$ 7,500,000,000
CEO and President
Unusual or Infrequent Item, or Both [Line Items]
Voluntary pay reduction																100.00%
Non-Employee Directors
Unusual or Infrequent Item, or Both [Line Items]
Voluntary pay reduction																100.00%
United Airlines, Inc.
Unusual or Infrequent Item, or Both [Line Items]
Net income (loss)																$ (7,067,000,000)	3,011,000,000	2,123,000,000
Proceeds from issuance of debt																16,044,000,000	$ 1,847,000,000	$ 1,594,000,000
United Airlines, Inc. | Secured Debt | Revolving Credit Facility
Unusual or Infrequent Item, or Both [Line Items]
Proceeds from lines of credit		$ 1,000,000,000.0														1,000,000,000.0
Credit agreement								$ 2,000,000,000.0								$ 2,000,000,000.0