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WORLDWIDE PANDEMIC - Narrative (Details) |  |  |  |  |  |  |  |  |  |  |  |  | 2 Months Ended | 3 Months Ended | 5 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended | 14 Months Ended
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Apr. 23, 2026 | Jan. 15, 2026 | Jun. 03, 2021 USD ($) shares | Apr. 23, 2021 USD ($) shares | Mar. 05, 2021 USD ($) shares | Jan. 15, 2021 USD ($) shares | Sep. 30, 2020 USD ($) shares | Jul. 30, 2020 USD ($) shares | Jun. 30, 2020 USD ($) shares | Jun. 01, 2020 employee | May 29, 2020 USD ($) shares | Apr. 21, 2020 USD ($) shares | Jun. 30, 2021 USD ($) employee supportProgram aircraft $ / shares shares | Sep. 30, 2021 USD ($) | Jun. 30, 2021 USD ($) employee supportProgram aircraft $ / shares shares | Mar. 31, 2021 USD ($) | Jun. 30, 2020 USD ($) shares | Sep. 30, 2020 USD ($) shares | Jun. 30, 2021 USD ($) employee supportProgram aircraft $ / shares shares | Jun. 30, 2021 USD ($) supportProgram aircraft employee $ / shares shares | Jun. 30, 2020 USD ($) shares | Dec. 31, 2020 USD ($) shares | Dec. 31, 2020 USD ($) shares | Jun. 30, 2021 USD ($) employee supportProgram aircraft $ / shares shares
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Promissory Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 |  | $ 2,683,000,000 |  |  | $ 0 | $ 3,683,000,000 |  |  |
Payroll support and voluntary Employee programs, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 740,000,000 |  | $ 784,000,000 |  |  | 2,187,000,000 | $ 784,000,000 |  |  |
Deferred Payroll Support Program grant proceeds |  |  |  |  |  |  |  |  |  |  |  |  | $ 763,000,000 |  | $ 763,000,000 |  |  |  | $ 763,000,000 | $ 763,000,000 |  | $ 0 | $ 0 | $ 763,000,000
COVID - 19 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of support programs | supportProgram |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  | 3 |  |  |  | 3 | 3 |  |  |  | 3
Voluntary separation program 2020 participants | employee |  |  |  |  |  |  |  |  |  |  |  |  | 4,200 |  | 4,200 |  |  |  | 4,200 | 4,200 |  |  |  | 4,200
Number of days before the end of their term |  |  |  |  |  |  |  |  |  | 90 days |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employees who elected conversion in extended emergency time off | employee |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300 |  |  |  |
Number of employees who participated in extended emergency time off during 2020 | employee |  |  |  |  |  |  |  |  |  | 11,000 |  |  | 7,000 |  | 7,000 |  |  |  | 7,000 | 7,000 |  |  |  | 7,000
Total employees who participated in extended emergency time off During 2020, who were still on emergency time off at December 31, 2020 | employee |  |  |  |  |  |  |  |  |  | 1,466 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extended emergency time off reversal for employees who accepted through March 31, 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 15,000,000 | $ 115,000,000 |  |  |  |  |  |  |  |
Proceeds from PSP2 payroll support program |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 724,000,000 |  |  |  |  | $ 1,900,000,000 |  |  |  |
Extended emergency time off accrual for employees who accepted through 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 436,000,000 | $ 348,000,000 |  |  |  |  |  |  | 1,400,000,000 |
Aircrafts in long-term storage | aircraft |  |  |  |  |  |  |  |  |  |  |  |  | 39 |  | 39 |  |  |  | 39 | 39 |  |  |  | 39
COVID - 19 | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extended emergency time off, period |  |  |  |  |  |  |  |  |  | 6 months |  |  |  |  |  |  |  |  |  |  |  |  |  |
COVID - 19 | Minimum | Option to Convert to Voluntary Separation Program 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extended emergency time off, period |  |  |  |  |  |  |  |  |  | 12 months |  |  |  |  |  |  |  |  |  |  |  |  |  |
Years of service |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
COVID - 19 | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extended emergency time off, period |  |  |  |  |  |  |  |  |  | 18 months |  |  |  |  |  |  |  |  |  |  |  |  |  |
COVID - 19 | Maximum | Option to Convert to Voluntary Separation Program 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extended emergency time off, period |  |  |  |  |  |  |  |  |  | 18 months |  |  |  |  |  |  |  |  |  |  |  |  |  |
COVID - 19 | Maximum | Pilots |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extended emergency time off, period |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
United States Department of Treasury | Subsequent Event | Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payroll support and voluntary Employee programs, net |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 763,000,000 |  |  |  |  |  |  |  |  |  |
United States Department of Treasury | COVID - 19 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total Payroll Support Proceeds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7,193,000,000
Promissory Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,068,000,000
Warrants ($) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 85,000,000
Warrants (shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  | 4,798,000 |  | 4,798,000 |  |  |  | 4,798,000 | 4,798,000 |  |  |  | 4,798,000
United States Department of Treasury | PSP1 Payroll Support Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total Payroll Support Proceeds |  |  |  |  |  |  | $ 94,000,000 | $ 326,000,000 | $ 652,000,000 |  | $ 652,000,000 | $ 1,630,000,000 |  |  |  |  |  | $ 3,354,000,000 |  |  |  | 3,400,000,000 |  |
Warrants and rights outstanding |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 40,000,000 | $ 40,000,000 |
Class of warrants or rights outstanding (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,700,000 | 2,700,000 |
Promissory Note |  |  |  |  |  |  | 28,000,000 | 97,000,000 | 196,000,000 |  | 196,000,000 | 459,000,000 |  |  |  |  |  | 976,000,000 |  |  |  |  |  |
Warrants ($) |  |  |  |  |  |  | $ 2,000,000 | $ 3,000,000 | $ 9,000,000 |  | $ 8,000,000 | $ 18,000,000 |  |  |  |  |  | $ 40,000,000 |  |  |  |  |  |
Warrants (shares) | shares |  |  |  |  |  |  | 78,000 | 268,000 | 536,000 |  | 536,000 | 1,258,000 |  |  |  |  | 536,000 | 78,000 |  |  | 536,000 | 2,676,000 | 2,676,000 |
United States Department of Treasury | PSP1 Payroll Support Program | Notes Payable, Other Payables |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 976,000,000 | $ 976,000,000 |
United States Department of Treasury | PSP2 Payroll Support Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total Payroll Support Proceeds |  |  |  | $ 259,000,000 | $ 864,000,000 | $ 864,000,000 |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,987,000,000 | $ 2,000,000,000.0 |  |  |  |
Warrants and rights outstanding |  |  |  |  |  |  |  |  |  |  |  |  | $ 27,000,000 |  | $ 27,000,000 |  |  |  | $ 27,000,000 | $ 27,000,000 |  |  |  | $ 27,000,000
Class of warrants or rights outstanding (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  | 1,200,000 |  | 1,200,000 |  |  |  | 1,200,000 | 1,200,000 |  |  |  | 1,200,000
Promissory Note |  |  |  | 78,000,000 | 259,000,000 | 229,000,000 |  |  |  |  |  |  |  |  |  |  |  |  | $ 566,000,000 |  |  |  |  |
Warrants ($) |  |  |  | $ 4,000,000 | $ 14,000,000 | $ 9,000,000 |  |  |  |  |  |  |  |  |  |  |  |  | $ 27,000,000 |  |  |  |  |
Warrants (shares) | shares |  |  |  | 168,000 | 560,000 | 495,000 |  |  |  |  |  |  | 1,223,000 |  | 1,223,000 |  |  |  | 1,223,000 | 1,223,000 |  |  |  | 1,223,000
Strike price (in USD per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 46.28 |  | $ 46.28 |  |  |  | $ 46.28 | $ 46.28 |  |  |  | $ 46.28
Expiration period (in years) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |
United States Department of Treasury | PSP2 Payroll Support Program | Notes Payable, Other Payables |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 566,000,000 |  | $ 566,000,000 |  |  |  | $ 566,000,000 | $ 566,000,000 |  |  |  | $ 566,000,000
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 1.00% |  | 1.00% |  |  |  | 1.00% | 1.00% |  |  |  | 1.00%
United States Department of Treasury | PSP2 Payroll Support Program | Notes Payable, Other Payables | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable rate (as a percent) |  | 2.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
United States Department of Treasury | PSP3 Payroll Support Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total Payroll Support Proceeds |  |  | $ 926,000,000 | $ 926,000,000 |  |  |  |  |  |  |  |  | $ 1,852,000,000 |  | $ 1,900,000,000 |  |  |  |  |  |  |  |  |
Warrants and rights outstanding |  |  |  |  |  |  |  |  |  |  |  |  | $ 18,000,000 |  | $ 18,000,000 |  |  |  | $ 18,000,000 | $ 18,000,000 |  |  |  | $ 18,000,000
Class of warrants or rights outstanding (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  | 899,000 |  | 899,000 |  |  |  | 899,000 | 899,000 |  |  |  | 899,000
Promissory Note |  |  | 278,000,000 | 248,000,000 |  |  |  |  |  |  |  |  | $ 526,000,000 |  |  |  |  |  |  |  |  |  |  |
Warrants ($) |  |  | $ 9,000,000 | $ 9,000,000 |  |  |  |  |  |  |  |  | $ 18,000,000 |  |  |  |  |  |  |  |  |  |  |
Warrants (shares) | shares |  |  | 475,000 | 424,000 |  |  |  |  |  |  |  |  | 899,000 |  | 899,000 |  |  |  | 899,000 | 899,000 |  |  |  | 899,000
Strike price (in USD per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 58.51 |  | $ 58.51 |  |  |  | $ 58.51 | $ 58.51 |  |  |  | $ 58.51
Expiration period (in years) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |
United States Department of Treasury | PSP3 Payroll Support Program | Notes Payable, Other Payables |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 526,000,000 |  | $ 526,000,000 |  |  |  | $ 526,000,000 | $ 526,000,000 |  |  |  | $ 526,000,000
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 1.00% |  | 1.00% |  |  |  | 1.00% | 1.00% |  |  |  | 1.00%
United States Department of Treasury | PSP3 Payroll Support Program | Notes Payable, Other Payables | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unusual or Infrequent Item, or Both [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable rate (as a percent) | 2.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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