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Financial Derivative Instruments - Location and Amount Recognized in Income by Hedging Relationship (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Cash Flow Hedging |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | $ 186 | $ 9 | $ 279 | $ (107)
Cash Flow Hedging | Fuel derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | 192 | 9 | 275 | (75)
Cash Flow Hedging | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | (6) | 0 | 4 | (32)
Fuel and oil |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments | 12 | 14 | 28 | 36
Fuel and oil | Cash Flow Hedging | Fuel derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | 12 | 14 | 28 | 36
Fuel and oil | Cash Flow Hedging | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | 0 | 0 | 0 | 0
Fuel and oil | Fair Value Hedging | Not Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Hedged items | 0 | 0 | 0 | 0
Fuel and oil | Fair Value Hedging | Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments | 0 | 0 | 0 | 0
Other (gains)/losses, net |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments | 0 | 14 | 6 | 16
Other (gains)/losses, net | Cash Flow Hedging | Fuel derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | 0 | 14 | 6 | 16
Other (gains)/losses, net | Cash Flow Hedging | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | 0 | 0 | 0 | 0
Other (gains)/losses, net | Fair Value Hedging | Not Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Hedged items | 0 | 0 | 0 | 0
Other (gains)/losses, net | Fair Value Hedging | Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments | 0 | 0 | 0 | 0
Other operating expenses |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments | 1 |  |  |
Other operating expenses | Cash Flow Hedging | Fuel derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | 0 |  |  |
Other operating expenses | Cash Flow Hedging | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | 1 |  |  |
Other operating expenses | Fair Value Hedging | Not Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Hedged items | 0 |  |  |
Other operating expenses | Fair Value Hedging | Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments | $ 0 |  |  |
Interest expense |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments |  | 3 | 2 | 4
Interest expense | Cash Flow Hedging | Fuel derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income |  | 0 | 0 | 0
Interest expense | Cash Flow Hedging | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income |  | 1 | 2 | 1
Interest expense | Fair Value Hedging | Not Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Hedged items |  | 4 | 0 | 7
Interest expense | Fair Value Hedging | Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments |  | $ (2) | $ 0 | $ (4)

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