Debt - Details of Pass Through Trusts (Details) - USD ($)	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Debt Instrument [Line Items]
Total proceeds received from issuance of debt	$ 1,669,000,000	$ 996,000,000
United Airlines, Inc.
Debt Instrument [Line Items]
Total proceeds received from issuance of debt	1,669,000,000	$ 996,000,000
Pass-Through Certificates \| United Airlines, Inc.
Debt Instrument [Line Items]
Face Amount	1,221,000,000
Total proceeds received from issuance of debt	328,000,000
Total debt recorded	1,221,000,000
Pass-Through Certificates \| Class AA Pass-Through Certificates Issued September 2019 \| United Airlines, Inc.
Debt Instrument [Line Items]
Face Amount	$ 702,000,000
Stated interest rate	2.70%
Total proceeds received from issuance of debt	$ 189,000,000
Total debt recorded	702,000,000
Pass-Through Certificates \| Class A Pass-Through Certificates Issued September 2019 \| United Airlines, Inc.
Debt Instrument [Line Items]
Face Amount	$ 287,000,000
Stated interest rate	2.90%
Total proceeds received from issuance of debt	$ 77,000,000
Total debt recorded	287,000,000
Pass-Through Certificates \| Class B Pass-Through Certificates Issued September 2019 \| United Airlines, Inc.
Debt Instrument [Line Items]
Face Amount	$ 232,000,000
Stated interest rate	3.50%
Total proceeds received from issuance of debt	$ 62,000,000
Total debt recorded	$ 232,000,000

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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