Commitments and Contingencies - Narrative (Details) $ / shares in Units, Employee in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Employee commitment aircraft Option Aircraft	Nov. 29, 2018 USD ($) $ / shares shares	Feb. 28, 2018 USD ($)
Commitments and Contingencies [Line Items]
Aggregate balance	$ 11,300,000,000
Number of call options to purchase regional jet aircraft | Option	292
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Debt instrument principal amount	$ 424,000,000
Number of employees | Employee	92
Percentage of employees represented by various U.S. labor organizations	83.00%
Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	$ 1,900,000,000.0
Operating leases obligations	1,300,000,000
Capital leases obligations	466,000,000
Tax-Exempt Special Facilities Revenue Bonds | Indirect Guarantee of Indebtedness
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	164,000,000
Contingent liabilities based on participation	1,700,000,000
Floating Rate Debt
Commitments and Contingencies [Line Items]
Debt instrument principal amount	3,500,000,000.0
Fixed Rate Debt
Commitments and Contingencies [Line Items]
Debt instrument principal amount	27,000,000
Loans And Leases From Non U S Entities
Commitments and Contingencies [Line Items]
Aggregate balance	3,200,000,000
Aircraft Mortgage Debt
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	$ 145,000,000
Minimum | Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Maturity date	2019
Minimum | Tax-Exempt Special Facilities Revenue Bonds | Indirect Guarantee of Indebtedness
Commitments and Contingencies [Line Items]
Maturity date	2022
Maximum
Commitments and Contingencies [Line Items]
Debt instrument, remaining terms	12 years
Maximum | Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Maturity date	2038
Maximum | Tax-Exempt Special Facilities Revenue Bonds | Indirect Guarantee of Indebtedness
Commitments and Contingencies [Line Items]
Maturity date	2051
Maximum | Loans And Leases From Non U S Entities
Commitments and Contingencies [Line Items]
Debt instrument, remaining terms	12 years
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 to 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		$ 217,200,000
Contingent liabilities based on participation		$ 31,000,000
EETC
Commitments and Contingencies [Line Items]
Debt instrument principal amount			$ 1,000,000,000.0
EETC | United Airlines, Inc.
Commitments and Contingencies [Line Items]
Debt instrument principal amount	$ 2,174,000,000
Embraer E175
Commitments and Contingencies [Line Items]
Number of aircrafts expects to take delivery | Aircraft	25
Number of firm commitments | commitment	25
Boeing 737 MAX
Commitments and Contingencies [Line Items]
Number of aircrafts expects to take delivery | Aircraft	20
Boeing 787
Commitments and Contingencies [Line Items]
Number of aircrafts expects to take delivery | Aircraft	8
Boeing 777-300ER
Commitments and Contingencies [Line Items]
Number of aircraft expected to be delivered | aircraft	2
Airbus A319s
Commitments and Contingencies [Line Items]
Number of firm commitments | aircraft	20
Embraer ERJ 145
Commitments and Contingencies [Line Items]
Number of aircraft under lease | aircraft	54