Debt - Details of Past Through Trusts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Feb. 28, 2018
Debt Instrument [Line Items]
Proceeds received from issuance of debt	$ 1,740,000,000	$ 2,765,000,000	[1]	$ 808,000,000	[1]
EETC
Debt Instrument [Line Items]
Principal						$ 1,000,000,000.0
United Airlines, Inc.
Debt Instrument [Line Items]
Principal	424,000,000
Proceeds received from issuance of debt	1,740,000,000	$ 2,765,000,000	[2]	$ 808,000,000	[2]
United Airlines, Inc. | EETC
Debt Instrument [Line Items]
Principal	2,174,000,000
Total debt recorded	1,161,000,000
Proceeds received from issuance of debt	1,161,000,000
Remaining proceeds from issuance of debt to be received in future periods	1,013,000,000
United Airlines, Inc. | AA | February 2019
Debt Instrument [Line Items]
Principal	$ 717,000,000
Stated interest rate	4.15%
Total debt recorded	$ 0
Proceeds received from issuance of debt	0
Remaining proceeds from issuance of debt to be received in future periods	717,000,000
United Airlines, Inc. | AA | February 2018
Debt Instrument [Line Items]
Principal	$ 677,000,000
Stated interest rate	3.50%
Total debt recorded	$ 677,000,000
Proceeds received from issuance of debt	677,000,000
Remaining proceeds from issuance of debt to be received in future periods	0
United Airlines, Inc. | A
Debt Instrument [Line Items]
Principal	$ 296,000,000
Stated interest rate	4.55%
Total debt recorded	$ 0
Proceeds received from issuance of debt	0
Remaining proceeds from issuance of debt to be received in future periods	296,000,000
United Airlines, Inc. | A | February 2018
Debt Instrument [Line Items]
Principal	$ 258,000,000
Stated interest rate	3.70%
Total debt recorded	$ 258,000,000
Proceeds received from issuance of debt	258,000,000
Remaining proceeds from issuance of debt to be received in future periods	0
United Airlines, Inc. | B | May 2018
Debt Instrument [Line Items]
Principal	$ 226,000,000
Stated interest rate	4.60%
Total debt recorded	$ 226,000,000
Proceeds received from issuance of debt	226,000,000
Remaining proceeds from issuance of debt to be received in future periods	$ 0

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606). See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.

[2] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606). See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.