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Revenue - Air Traffic Liability Rollforward (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Air Traffic Liability Roll Forward    
ATL, beginning balance $ 5,510 $ 5,070
Current Period Sales 7,631 16,410
Revenue amounts in beginning balance (2,126) (3,160)
Revenue from Current Period Sales (3,921) (12,354)
ATL, ending balance $ 7,094 $ 5,966