Revenue Recognition - Loyalty Program Liability (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Frequent Flyer Liability Activity [Roll Forward]
Miles earned	$ 660	$ 720
Travel miles redeemed	(543)	(692)
Non-travel miles redeemed	(28)	(45)
Loyalty program
Frequent Flyer Liability Activity [Roll Forward]
Deferred revenue (current and noncurrent), beginning	6,728	6,641
Deferred revenue (current and noncurrent), ending	$ 6,817	$ 6,624

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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130531-203044

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130549-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130532-203044

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant