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Revenue - Roll Forward of Frequent Flyer Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Frequent Flyer Deferred Revenue [Roll Forward] |  |  |  |
Total Frequent flyer deferred revenue - beginning balance | $ 5,138 | $ 4,937 | $ 5,005 | $ 4,783
Miles awarded | 682 | 607 | 1,289 | 1,210
Travel miles redeemed (Passenger revenue) | (589) | (519) | (1,027) | (928)
Non-travel miles redeemed (Other operating revenue) | (33) | (36) | (69) | (76)
Total Frequent flyer deferred revenue - ending balance | $ 5,198 | $ 4,989 | $ 5,198 | $ 4,989

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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/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 + Details
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