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Revenue - Roll Forward of Frequent Flyer Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Frequent Flyer Deferred Revenue [Roll Forward] |  |  |  |
Total Frequent flyer deferred revenue - beginning balance | $ 6,185 | $ 5,670 | $ 5,975 | $ 5,276
Total miles awarded | 439 | 268 | 1,071 | 1,056
Travel miles redeemed (Passenger revenue) | (391) | (87) | (781) | (444)
Non-travel miles redeemed (Other operating revenue) | (16) | (16) | (48) | (53)
Total Frequent flyer deferred revenue - ending balance | $ 6,217 | $ 5,835 | $ 6,217 | $ 5,835

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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=123360276&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=123351226&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=123360276&loc=SL49130532-203044 + Details
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