Revenue - Summary of Roll Forward of Frequent Flyer Deferred Revenue (Details) - Deferred Revenue for Miles in Loyalty Program - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Movement in Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 4,989	$ 4,891	$ 4,783	$ 4,889
Total miles awarded	616	525	1,826	1,544
Travel miles redeemed (Passenger revenue)	(580)	(556)	(1,508)	(1,489)
Non-travel miles redeemed (Other operating revenue)	(38)	(42)	(114)	(126)
Total Frequent flyer deferred revenue - ending balance	$ 4,987	$ 4,818	$ 4,987	$ 4,818

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130532-203044

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130549-203045

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130531-203044

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