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COMMITMENTS, CONTINGENCIES AND GUARANTEES - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) employee aircraft option	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Commitments and Contingencies [Line Items]
Carrying amount of loan receivable	$ 72
Liabilities due	$ 4,193	$ 3,835
Number of call options to purchase regional jet aircraft \| option	207
Aggregate balance	$ 5,178
Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Underlying debt and interest	2,900
Tax-Exempt Special Facilities Revenue Bonds \| Indirect Guarantee of Indebtedness
Commitments and Contingencies [Line Items]
Underlying debt and interest	504
Contingent liabilities based on participation	2,700
Floating Rate Debt
Commitments and Contingencies [Line Items]
Long term debt	$ 8,500
Debt instrument, remaining terms	12 years
Loans And Leases From Non-U.S. Entities
Commitments and Contingencies [Line Items]
Debt instrument, remaining terms	12 years
Aggregate balance	$ 5,300
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Liabilities due	$ 4,193	3,835
Number of employees \| employee	107,300
Percentage of employees represented by various U.S. labor organizations	82.00%
United Airlines, Inc. \| Surety Bonds
Commitments and Contingencies [Line Items]
Contingent liabilities based on participation	$ 396
United Airlines, Inc. \| Regional Aircraft \| Capacity Purchase Agreements
Commitments and Contingencies [Line Items]
Expenses related to CPAs	1,100	1,100	$ 900
United Airlines, Inc. \| Regional Aircraft \| Capacity Purchase Agreements \| Related Party
Commitments and Contingencies [Line Items]
Carrying amount of loan receivable	52	84
Liabilities due	$ 110	$ 122
United Airlines, Inc. \| Cash Collateralized Letters of Credit
Commitments and Contingencies [Line Items]
Number of regional aircraft \| aircraft	412