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Fair Value Measurements - Summary of Carrying Amounts and Estimated Fair Values of the Company’s Debt (Details) - USD ($) $ in Millions | Dec. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Carrying Value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | $ 620 | $ 507
Estimated Fair Value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 626 | 505
Pre-delivery Credit Facilities | Carrying Value | Secured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 348 | 329
Pre-delivery Credit Facilities | Estimated Fair Value | Secured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 352 | 333
Building notes | Carrying Value | Secured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 0 | 12
Building notes | Estimated Fair Value | Secured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 0 | 12
2025-1 EETCs | Carrying Value | Secured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 105 | 0
2025-1 EETCs | Estimated Fair Value | Secured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 109 | 0
Affinity card advance purchase of miles | Carrying Value | Unsecured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 101 | 100
Affinity card advance purchase of miles | Estimated Fair Value | Unsecured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 100 | 98
PSP Promissory Notes | Carrying Value | Unsecured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | 66 | 66
PSP Promissory Notes | Estimated Fair Value | Unsecured Debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total debt | $ 65 | $ 62

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