Commitments and Contingencies - Narrative (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) employee option
Commitments and Contingencies [Line Items]
Aggregate balance	$ 13,600,000,000
Number of call options to purchase regional jet aircraft | option	251
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Number of employees | employee	84,100
Percentage of employees represented by various U.S. labor organizations	85.00%
United Airlines, Inc. | Surety Bonds
Commitments and Contingencies [Line Items]
Contingent liabilities based on participation	$ 371,000,000
Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	2,100,000,000
Tax-Exempt Special Facilities Revenue Bonds | Indirect Guarantee of Indebtedness
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	343,000,000
Contingent liabilities based on participation	1,800,000,000
Aircraft Mortgage Debt
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	$ 106,000,000
Loans And Leases From Non U S Entities
Commitments and Contingencies [Line Items]
Debt instrument, remaining terms	11 years
Aggregate balance	$ 10,100,000,000
Floating Rate Debt
Commitments and Contingencies [Line Items]
Aggregate principal amount	$ 13,200,000,000
Debt instrument, remaining terms	11 years