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Schedule II - Valuation and Qualifying Accounts (Details) - UAL and United - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Allowance for doubtful accounts |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | $ 78 | $ 9 | $ 8
Additions Charged to Costs and Expenses | 3 | 70 | 17
Deductions | 53 | 16 | 16
Other | 0 | 15 | 0
Balance at End of Period | 28 | 78 | 9
Obsolescence allowance-spare parts |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 478 | 425 | 412
Additions Charged to Costs and Expenses | 79 | 88 | 76
Deductions | 11 | 35 | 63
Other | 0 | 0 | 0
Balance at End of Period | 546 | 478 | 425
Allowance for credit losses - notes receivable |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 522 | 0 |
Additions Charged to Costs and Expenses | 1 | 518 |
Deductions | 0 | 0 |
Other | 99 | 4 |
Balance at End of Period | 622 | 522 | 0
Valuation allowance for deferred tax assets |  |  |
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance at Beginning of Period | 247 | 58 | 59
Additions Charged to Costs and Expenses | (38) | 197 | 0
Deductions | 0 | 8 | 1
Other | 1 | 0 | 0
Balance at End of Period | $ 210 | $ 247 | $ 58

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- Definition Amount of valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09(Column B)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24092-122690 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09(Column E)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24092-122690 + Details
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