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Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Allowance for credit losses - receivables: |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | $ 11 | $ 28 | $ 78
Additions Charged to Costs and Expenses | 27 | 22 | 3
Deductions | 23 | 39 | 53
Other | 3 | 0 | 0
Balance at End of Period | 18 | 11 | 28
Allowance for credit losses - receivables: | United Airlines, Inc. |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 11 | 28 | 78
Additions Charged to Costs and Expenses | 27 | 22 | 3
Deductions | 23 | 39 | 53
Other | 3 | 0 | 0
Balance at End of Period | 18 | 11 | 28
Obsolescence allowance—spare parts: |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 610 | 546 | 478
Additions Charged to Costs and Expenses | 102 | 73 | 79
Deductions | 23 | 9 | 11
Other | 0 | 0 | 0
Balance at End of Period | 689 | 610 | 546
Obsolescence allowance—spare parts: | United Airlines, Inc. |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 610 | 546 | 478
Additions Charged to Costs and Expenses | 102 | 73 | 79
Deductions | 23 | 9 | 11
Other | 0 | 0 | 0
Balance at End of Period | 689 | 610 | 546
Allowance for credit losses - investments in affiliates and other: |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 21 | 622 | 522
Additions Charged to Costs and Expenses | 20 | 20 | 1
Deductions | 0 | 539 | 0
Other | (3) | (82) | 99
Balance at End of Period | 38 | 21 | 622
Allowance for credit losses - investments in affiliates and other: | United Airlines, Inc. |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 21 | 622 | 522
Additions Charged to Costs and Expenses | 20 | 20 | 1
Deductions | 0 | 539 | 0
Other | (3) | (82) | 99
Balance at End of Period | 38 | 21 | 622
Valuation allowance for deferred tax assets: |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 199 | 210 | 247
Additions Charged to Costs and Expenses | (21) | (10) | (38)
Deductions | 0 | 0 | 0
Other | 1 | (1) | 1
Balance at End of Period | 179 | 199 | 210
Valuation allowance for deferred tax assets: | United Airlines, Inc. |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 199 | 210 | 247
Additions Charged to Costs and Expenses | (21) | (10) | (38)
Deductions | 0 | 0 | 0
Other | 1 | (1) | 1
Balance at End of Period | $ 179 | $ 199 | $ 210

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