Commitments and Contingencies - Narrative (Details) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended
	Mar. 31, 2020 USD ($)	Jun. 30, 2020 USD ($) employee commitment aircraft	Jun. 30, 2020 USD ($) employee commitment aircraft	Apr. 17, 2020 aircraft	Dec. 31, 2018 USD ($)	Nov. 30, 2018 USD ($) $ / shares shares
Commitments and Contingencies [Line Items]
Remaining term of debt			12 years
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Number of employees | employee		91,800	91,800
Percentage of employees represented by various U.S. labor organizations			85.00%
Percentage of employees on voluntary unpaid leave of absence			22.00%
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		126	126
Floating Rate Debt
Commitments and Contingencies [Line Items]
Debt		7,600	$ 7,600
Loans and Leases from Non-U.S. Entities
Commitments and Contingencies [Line Items]
Remaining term of debt			12 years
Aggregate balance		$ 7,400	$ 7,400
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		13	13
Boeing 787
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment		16	16
Number of aircraft subject to purchase rights assignment agreement financed through a sale and leaseback transaction | aircraft				6
Number of aircraft delivered in period | aircraft		2
Number of aircraft scheduled to be delivered through the end of the year | aircraft		20	20
Boeing 737 MAX
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment		171	171
Number of aircraft subject to purchase rights assignment agreement financed through a sale and leaseback transaction | aircraft				16
Embraer E175
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment		20	20