Leases - Lease Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Finance lease cost, amortization of leased assets	$ 131	$ 131	$ 110
Finance lease cost, interest of lease liabilities	55	32	29
Operating lease cost	863	1,019	1,013
Short-term lease cost	245	264	500
Variable lease cost	1,599	1,406	1,456
Total lease cost	2,893	2,852	3,108
Regional carrier
Lessee, Lease, Description [Line Items]
Operating lease cost	111	187	174
Variable lease cost	$ 29	$ 50	$ 64