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Debt - Schedule of Debt Obligations (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2025 | Nov. 30, 2025 | Dec. 31, 2024 | Sep. 30, 2024 | Jun. 30, 2024
Debt Instrument [Line Items] |  |  |  |  |
Long-term debt, gross | $ 620 |  | $ 507 |  |
Less: current maturities of long-term debt, net | (301) |  | (261) |  |
Less: total debt acquisition costs and other discounts, net | (6) |  | (5) |  |
Long-term debt, net | $ 313 |  | $ 241 |  |
Periodic payment, interest, period (in days) | 90 days |  |  |  |
CARES Act Credit Agreement, Warrants |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Warrants to acquire common stock (in shares) | 237,274 |  | 3,117,940 |  |
Exercise price of warrants (in dollars per share) |  |  | $ 6.95 |  |
Warrants exercised (in shares) | 1,244,608 |  |  |  |
Number of securities called by warrants (in shares) | 248,893 |  |  |  |
Warrant settled, cash potion (less than) | $ 1 |  |  |  |
Warrants expired (in shares) | 1,636,058 |  |  |  |
Secured Debt | Revolving Credit Facility |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Long-term debt, gross | $ 0 |  | $ 0 |  |
Amount of unsecured borrowings available | 220 |  |  |  |
Secured Debt | Pre-delivery Credit Facilities |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Long-term debt, gross | 348 |  | 329 |  |
Amount of unsecured borrowings available | 391 |  |  |  |
Secured Debt | Building notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Long-term debt, gross | 0 |  | 12 |  |
Unsecured low interest loan amount |  |  |  | $ 12 |
Secured Debt | Building Note Tranche One |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Unsecured low interest loan amount |  |  |  |  | $ 6
Secured Debt | Building Note Tranche Two |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Unsecured low interest loan amount |  |  |  | $ 6 |
Secured Debt | 2025-1 EETCs |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Long-term debt, gross | 105 |  | 0 |  |
Secured Debt | Pass Through Certificates 2025-1 Class A |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Unsecured low interest loan amount |  | $ 105 |  |  |
Interest rate (as a percent) |  | 6.75% |  |  |
Unsecured Debt | Affinity card advance purchase of miles |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Long-term debt, gross | 101 |  | 100 |  |
Amount of unsecured borrowings available | $ 200 |  |  |  |
Term of principal repayments | 12 months |  |  |  |
Unsecured Debt | PSP Promissory Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Long-term debt, gross | $ 66 |  | $ 66 |  |
Interest rate (as a percent) | 1.00% |  |  |  |
Interest rate period (in years) | 5 years |  |  |  |
Variable rate (as a percent) | 2.00% |  |  |  |
Unsecured Debt | PSP1 Promissory Note |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Loan term (in years) | 10 years |  |  |  |

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