Operating Leases - Aircraft Rent Expense and Maintenance Obligations (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
Dec. 31, 2025 |
|
| Lessee, Lease, Description [Line Items] | |||||
| Aircraft rent expense | $ 301 | $ 181 | $ 832 | $ 536 | |
| Supplemental rent expense (benefit) related to probable lease return condition obligations | 97 | (1) | 218 | 2 | |
| Leased aircraft return cost liability | 229 | 229 | $ 19 | ||
| Aircraft | |||||
| Lessee, Lease, Description [Line Items] | |||||
| Gain lease extension | $ 13 | $ 7 | $ 17 | $ 27 | |