Commitments and Contingencies - Narrative (Details) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2020 USD ($) aircraft employee commitment	Mar. 31, 2020 USD ($) aircraft employee commitment	Apr. 17, 2020 aircraft	Dec. 31, 2018 USD ($)	Nov. 30, 2018 USD ($) $ / shares shares
Commitments and Contingencies [Line Items]
Remaining term of debt		11 years
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Number of employees | employee	95,200	95,200
Percentage of employees represented by various U.S. labor organizations		83.00%
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	$ 1,900
Aircraft Mortgage Debt
Commitments and Contingencies [Line Items]
Aggregate principal amount of guarantee	129	129
Floating Rate Debt
Commitments and Contingencies [Line Items]
Debt	6,000	$ 6,000
Loans and Leases from Non-U.S. Entities
Commitments and Contingencies [Line Items]
Remaining term of debt		11 years
Aggregate balance	$ 5,800	$ 5,800
Airbus A319
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | aircraft	20	20
Boeing 737-700
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | aircraft	18	18
Boeing 787
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment	19	19
Number of aircraft purchase options exercised | aircraft		7
Boeing 787 | Subsequent Event
Commitments and Contingencies [Line Items]
Number of aircraft subject to purchase rights assignment agreement | aircraft			6
Boeing 737 MAX
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment	171	171
Boeing 737 MAX | Subsequent Event
Commitments and Contingencies [Line Items]
Number of aircraft subject to purchase rights assignment agreement | aircraft			16
Embraer E175
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment	20	20
Number of aircraft no longer expected to be assigned | aircraft	20	20