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Fair Value Measurements - Measured on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Assets |  |
Treasury bills |  | $ 1,094
Fuel derivatives: |  |
Equity Securities | $ 433 | 367
Total assets | 3,451 | 9,222
Option contracts |  |
Fuel derivatives: |  |
Option contracts |  | 130
Certificates of deposit |  |
Assets |  |
Certificates of deposit | 16 | 122
Time deposits |  |
Assets |  |
Certificates of deposit | 100 |
Cash equivalents |  |
Assets |  |
Cash equivalents | 2,552 | 7,209
Time deposits |  |
Assets |  |
Cash equivalents | 350 | 300
Quoted prices in active markets for identical assets (Level 1) |  |
Assets |  |
Treasury bills |  | 1,094
Fuel derivatives: |  |
Equity Securities | 433 | 367
Total assets | 2,985 | 8,670
Quoted prices in active markets for identical assets (Level 1) | Option contracts |  |
Fuel derivatives: |  |
Option contracts |  | 0
Quoted prices in active markets for identical assets (Level 1) | Certificates of deposit |  |
Assets |  |
Certificates of deposit | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Time deposits |  |
Assets |  |
Certificates of deposit | 0 |
Quoted prices in active markets for identical assets (Level 1) | Cash equivalents |  |
Assets |  |
Cash equivalents | 2,552 | 7,209
Quoted prices in active markets for identical assets (Level 1) | Time deposits |  |
Assets |  |
Cash equivalents | 0 | 0
Significant other observable inputs (Level 2) |  |
Assets |  |
Treasury bills |  | 0
Fuel derivatives: |  |
Equity Securities | 0 | 0
Total assets | 466 | 422
Significant other observable inputs (Level 2) | Option contracts |  |
Fuel derivatives: |  |
Option contracts |  | 0
Significant other observable inputs (Level 2) | Certificates of deposit |  |
Assets |  |
Certificates of deposit | 16 | 122
Significant other observable inputs (Level 2) | Time deposits |  |
Assets |  |
Certificates of deposit | 100 |
Significant other observable inputs (Level 2) | Cash equivalents |  |
Assets |  |
Cash equivalents | 0 | 0
Significant other observable inputs (Level 2) | Time deposits |  |
Assets |  |
Cash equivalents | $ 350 | 300
Significant unobservable inputs (Level 3) |  |
Assets |  |
Treasury bills |  | 0
Fuel derivatives: |  |
Equity Securities |  | 0
Total assets |  | 130
Significant unobservable inputs (Level 3) | Option contracts |  |
Fuel derivatives: |  |
Option contracts |  | 130
Significant unobservable inputs (Level 3) | Certificates of deposit |  |
Assets |  |
Certificates of deposit |  | 0
Significant unobservable inputs (Level 3) | Cash equivalents |  |
Assets |  |
Cash equivalents |  | 0
Significant unobservable inputs (Level 3) | Time deposits |  |
Assets |  |
Cash equivalents |  | $ 0

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