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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
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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

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- Definition Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable. + References 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 + Details
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