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Schedule II - Valuation and Qualifying Accounts (Details) - UAL and United - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Allowance for doubtful accounts      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Period $ 28 $ 78 $ 9
Additions Charged to Costs and Expenses 22 3 70
Deductions 39 53 16
Other 0 0 15
Balance at End of Period 11 28 78
Obsolescence allowance-spare parts      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Period 546 478 425
Additions Charged to Costs and Expenses 73 79 88
Deductions 9 11 35
Other 0 0 0
Balance at End of Period 610 546 478
Allowance for credit losses - notes receivable      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Period 622 522 0
Additions Charged to Costs and Expenses 20 1 518
Deductions 539 0 0
Other (82) 99 4
Balance at End of Period 21 622 522
Valuation allowance for deferred tax assets      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Period 210 247 58
Additions Charged to Costs and Expenses (10) (38) 197
Deductions 0 0 8
Other (1) 1 0
Balance at End of Period $ 199 $ 210 $ 247