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Operating Leases - Aircraft Rent Expense and Maintenance Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Lessee, Lease, Description [Line Items] |  |  |
Aircraft rent expense | $ 748 | $ 675 | $ 554
Supplemental rent expense related to probable lease return condition obligations | 20 | 52 | 20
Leased aircraft return cost liability | 19 | 49 |
Proceeds from previously paid maintenance deposits |  | 104 |
Aircraft and spare engines |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Gain lease extension | $ 27 | $ 14 | $ 53

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