Operating Leases - Aircraft Rent Expense and Maintenance Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Aircraft rent expense	$ 530	$ 396	$ 368
Supplemental rent expense for maintenance-related reserves deemed non-recoverable	(3)	2	6
Supplemental rent expense related to probable lease return condition obligations	61	25	$ 5
Aircraft maintenance deposits expected to be recoverable	108	82
Aircraft maintenance deposits expected to be recoverable, eligible maintenance performed	10	1
Aircraft maintenance deposits	98	$ 82
Maintenance reserve payments, due in year one	3
Maintenance reserve payments, due in year two	3
Maintenance reserve payments, due in year three	3
Maintenance reserve payments, due in year four	3
Maintenance reserve payments, due in year five	3
Maintenance reserve payments, due after year five	$ 9