Revenue Recognition - Loyalty Program Liability (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Frequent Flyer Liability Activity [Roll Forward]
Mileage credits earned	$ 3,142	$ 2,948
Travel mileage credits redeemed	(2,651)	(2,403)
Non-travel mileage credits redeemed	(171)	(146)
Loyalty program
Frequent Flyer Liability Activity [Roll Forward]
Deferred revenue (current and noncurrent), beginning	6,321	5,922
Deferred revenue (current and noncurrent), ending	$ 6,641	$ 6,321

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

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