Consolidated Statements of Cash Flows - Reconciliation of Cash, Cash Equivalents, and Restricted Cash - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Cash Flows [Abstract]
Flight and ground equipment acquired under finance leases	$ 100	$ 261	$ 86
Current assets:
Cash and cash equivalents	1,565	1,814	2,762
Restricted cash included in prepaid expenses and other	47	39	64
Noncurrent assets:
Cash restricted for airport construction	1,136	0
Total cash, cash equivalents and restricted cash	$ 2,748	$ 1,853	$ 2,826