Commitments and Contingencies - Narrative (Details) $ / shares in Units, employee in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) aircraft employee commitment	Dec. 31, 2019 aircraft	Mar. 13, 2019 aircraft	Mar. 12, 2019 aircraft	Nov. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2018 aircraft
Commitments and Contingencies [Line Items]
Remaining term of debt	12 years
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Number of employees | employee	93
Percentage of employees represented by various U.S. labor organizations	84.00%
Kingsland
Commitments and Contingencies [Line Items]
Number of shares that may be put to United (in shares) | shares					144,800,000.0
Number of ADRs that may be put into United (in shares) | shares					18,100,000
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
Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Aggregate principal amount of guarantee | $	$ 1,900
Floating Rate Debt
Commitments and Contingencies [Line Items]
Debt | $	3,400
Fixed Rate Debt
Commitments and Contingencies [Line Items]
Debt | $	$ 18
Loans and Leases from Non-U.S. Entities
Commitments and Contingencies [Line Items]
Remaining term of debt	12 years
Aggregate balance | $	$ 3,200
Aircraft Mortgage Debt
Commitments and Contingencies [Line Items]
Aggregate principal amount of guarantee | $	$ 142
Embraer E175
Commitments and Contingencies [Line Items]
Number of aircraft expected to take delivery of in 2019	25
Number of aircraft committed to purchase | commitment	25
Boeing 737 MAX
Commitments and Contingencies [Line Items]
Number of aircraft expected to take delivery of in 2019	16
Number of aircraft expected to take delivery of in 2020	28
Number of aircraft committed to purchase | commitment	171
Number of aircraft grounded under emergency order			14
Number of flights operated using grounded aircraft				50
Boeing 737 MAX | Forecast
Commitments and Contingencies [Line Items]
Number of expected flights operating per day prior to grounding order		110
Boeing 787
Commitments and Contingencies [Line Items]
Number of aircraft expected to take delivery of in 2019	4
Number of aircraft expected to take delivery of in 2020	15
Number of aircraft committed to purchase | commitment	20
Boeing 777-300ER
Commitments and Contingencies [Line Items]
Number of aircraft expected to take delivery of in 2019	2
Number of aircraft expected to take delivery of in 2020	2
Airbus A319
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase	20
Embraer ERJ 145
Commitments and Contingencies [Line Items]
Number of leased aircraft						54