Debt - Details of Pass Through Trusts (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Debt Instrument [Line Items]
Total proceeds received from issuance of debt	$ 1,336,000,000	$ 2,813,000,000
United Airlines, Inc.
Debt Instrument [Line Items]
Total proceeds received from issuance of debt	1,336,000,000	$ 2,813,000,000
Pass-Through Certificates \| Class A Pass-Through Certificates Issued February 2021 \| United Airlines, Inc.
Debt Instrument [Line Items]
Face Amount	$ 600,000,000
Stated interest rate	4.88%
Total proceeds received from issuance of debt	$ 600,000,000
Total debt recorded	$ 600,000,000

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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