Commitments and Contingencies - Narrative (Details) $ / shares in Units, shares in Millions, $ in Millions		1 Months Ended	9 Months Ended
	Sep. 28, 2020	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) commitment employee aircraft	Dec. 31, 2018 USD ($)	Nov. 30, 2018 USD ($) $ / shares shares
Commitments and Contingencies [Line Items]
Remaining term of debt			12 years
Minimum years of service for early separation option	10 years
Minimum employee age for early separation option	50 years
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Number of employees | employee			87,887
Percentage of employees represented by various U.S. labor organizations			85.00%
Percentage of employees on voluntary unpaid leave of absence			52.00%
Kingsland
Commitments and Contingencies [Line Items]
Number of shares that may be put to United (in shares) | shares					144.8
Number of ADRs that may be put into United (in shares) | shares					18.1
Market price of common stock at fifth anniversary (in dollars per share) | $ / shares					$ 12
Aggregate maximum possible combined put payment and guarantee amount					$ 217
Liability for the fair value of guarantees				$ 31
Additional expense recorded for guarantee		$ 182
Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Aggregate principal amount of guarantee			$ 1,900
Aircraft Mortgage Debt
Commitments and Contingencies [Line Items]
Aggregate principal amount of guarantee			123
Floating Rate Debt
Commitments and Contingencies [Line Items]
Debt			$ 12,300
Loans and Leases from Non-U.S. Entities
Commitments and Contingencies [Line Items]
Remaining term of debt			12 years
Aggregate balance			$ 10,800
Airbus A319
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment			20
Boeing 737-700
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment			11
Boeing 787
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment			11
Number of aircraft delivered in period | aircraft			7
Boeing 737 MAX
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment			171
Embraer E175
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment			15
Grounded Aircraft Indebtedness
Commitments and Contingencies [Line Items]
Approximate possible loss			$ 450