Operating Leases - Aircraft Rent Expense and Maintenance Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Lessee, Lease, Description [Line Items]
Aircraft rent expense	$ 675	$ 554	$ 556
Supplemental rent expense for maintenance-related reserves deemed non-recoverable	(7)	(2)	(1)
Supplemental rent expense related to probable lease return condition obligations	52	20	$ 90
Leased aircraft return cost liability	49	26
Maintenance deposit refund	104
Rent benefit related to previously accrued lease return costs		$ 53
Aircraft and spare engines
Lessee, Lease, Description [Line Items]
Gain (loss) on renewal of lease	$ 14