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Financial Derivative Instruments - Location and Amount Recognized in Income by Hedging Relationship (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2021 | Dec. 31, 2020
Cash Flow Hedging |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | $ (463) | $ 106 |  |
Cash Flow Hedging | Fuel derivative contracts |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | (461) | 80 |  |
Cash Flow Hedging | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income | $ (2) | $ 26 |  |
Fuel and oil |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments |  |  | $ 4 | $ 70
Fuel and oil | Cash Flow Hedging | Fuel derivative contracts |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income |  |  | 4 | 70
Fuel and oil | Cash Flow Hedging | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income |  |  | 0 | 0
Fuel and oil | Fair Value Hedging | Not Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Hedged items |  |  | 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
Other (gains)/losses, net |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments |  |  | 6 | 39
Other (gains)/losses, net | Cash Flow Hedging | Fuel derivative contracts |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income |  |  | 6 | 39
Other (gains)/losses, net | Cash Flow Hedging | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income |  |  | 0 | 0
Other (gains)/losses, net | Fair Value Hedging | Not Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Hedged items |  |  | 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
Other operating expenses |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments |  |  | 6 |
Other operating expenses | Cash Flow Hedging | Fuel derivative contracts |  |  |  |
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 |  |  | 6 |
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 |  |  |  | 6
Interest expense | Cash Flow Hedging | Fuel derivative contracts |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income |  |  |  | 0
Interest expense | Cash Flow Hedging | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Amount of loss reclassified from AOCI into income |  |  |  | 1
Interest expense | Fair Value Hedging | Not Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Hedged items |  |  |  | 11
Interest expense | Fair Value Hedging | Designated as Hedging Instrument | Interest rate derivatives |  |  |  |
Derivative [Line Items] |  |  |  |
Derivatives designated as hedging instruments |  |  |  | $ (6)

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