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Financial Derivative Instruments - Premiums for Fuel Derivative Contracts (Details) - Fuel derivatives - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Designated as Hedging Instrument | Operating Expense [Member] |  |  |  |
Derivative [Line Items] |  |  |  |
Premiums paid for fuel derivative contracts | $ 13 | $ 20 | $ 51 | $ 75
Not Designated as Hedging Instrument | Other (gains)/losses, net |  |  |  |
Derivative [Line Items] |  |  |  |
Premiums paid for fuel derivative contracts | $ 11 | $ 0 | $ 22 | $ 0

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