Revenue - Summary of Roll Forward of Frequent Flyer Deferred Revenue (Details) - Deferred Revenue for Miles in Loyalty Program - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Movement in Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 4,937	$ 4,940	$ 4,783	$ 4,889
Total miles awarded	607	531	1,210	1,019
Travel miles redeemed (Passenger revenue)	(519)	(535)	(928)	(933)
Non-travel miles redeemed (Other operating revenue)	(36)	(45)	(76)	(84)
Total Frequent flyer deferred revenue - ending balance	$ 4,989	$ 4,891	$ 4,989	$ 4,891

Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 13.A.3)
-URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 13.A.4(a).Q1)
-URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780

Name:	us-gaap_DeferredRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant