Combined Notes to the Financial Statements (Unaudited) (Details) employee in Thousands					1 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 28, 2020 USD ($)	Jul. 02, 2020 USD ($)	Apr. 21, 2020 USD ($)	Apr. 20, 2020 USD ($)	Jul. 31, 2020 employee	Dec. 31, 2020	Sep. 30, 2020 USD ($) employee	Sep. 30, 2019 USD ($)	Jul. 02, 2020 USD ($)	Sep. 30, 2020 USD ($) employee	Sep. 30, 2019 USD ($)	Oct. 31, 2020 USD ($)	Jun. 15, 2020 shares
Unusual or Infrequent Item, or Both [Line Items]
Net income (loss)							$ (1,841,000,000)	$ 1,024,000,000		$ (5,172,000,000)	$ 2,368,000,000
Percent of capacity cut							70.00%
Rolling cancellation period										60 days
Proceeds from issuance of debt										$ 13,024,000,000	1,109,000,000
Proceeds from the issuance of common stock			$ 1,100,000,000							1,100,000,000
Payroll taxes deferred under the CARES Act										$ 140,000,000
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			$ 5,100,000,000			$ 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
Portion of grant recognized as a credit to special charges							1,494,000,000	0		3,083,000,000	0
Deferred credit							453,000,000			453,000,000
Forecast
Unusual or Infrequent Item, or Both [Line Items]
Percent of capacity cut						55.00%
Treasury Loan | Line of Credit
Unusual or Infrequent Item, or Both [Line Items]
Maximum capacity under loan facility (up to)	$ 5,200,000,000
Treasury Loan | Line of Credit | Forecast
Unusual or Infrequent Item, or Both [Line Items]
Maximum capacity under loan facility (up to)												$ 7,500,000,000
Equity Distribution Agreement
Unusual or Infrequent Item, or Both [Line Items]
Proceeds from the issuance of common stock										22,000,000
Number of shares issuable under Equity Distribution Agreement (up to) (in shares) | shares													28,000,000
Notes, Secured Term Loans and Aircraft Financing
Unusual or Infrequent Item, or Both [Line Items]
Proceeds from issuance of debt									$ 10,200,000,000
Secured Debt | PSP Note
Unusual or Infrequent Item, or Both [Line Items]
Face amount							$ 1,500,000,000			1,500,000,000
Unsecured Debt | PSP Note
Unusual or Infrequent Item, or Both [Line Items]
Term of debt				10 years			10 years
Line of Credit | Treasury Loan
Unusual or Infrequent Item, or Both [Line Items]
Proceeds from issuance of debt	520,000,000
Maximum capacity under loan facility (up to)	5,200,000,000
Face amount	$ 520,000,000
U.S. Department of Treasury Warrants
Unusual or Infrequent Item, or Both [Line Items]
Warrants oustanding							$ 66,000,000			$ 66,000,000
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)							$ (1,841,000,000)	$ 1,024,000,000		$ (5,171,000,000)	2,369,000,000
Proceeds from issuance of debt										$ 13,024,000,000	$ 1,109,000,000
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
Maximum capacity under loan facility (up to)		$ 2,000,000,000.0							$ 2,000,000,000.0