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Financial Derivative Instruments - Offsetting of Derivative Liabilities (Details) - USD ($) $ in Millions | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Fuel derivatives | Prepaid expenses and other current assets |  |  |
Offsetting Liabilities [Line Items] |  |  |
Gross amounts of recognized liabilities |  | $ 15 | $ 3
Gross asset amounts offset in the Balance Sheet |  | (15) | (3)
Liability derivative contracts, net |  | 0 | 0
Fuel derivatives | Other Assets |  |  |
Offsetting Liabilities [Line Items] |  |  |
Gross amounts of recognized liabilities |  | 57 | 31
Gross asset amounts offset in the Balance Sheet |  | (57) | (31)
Liability derivative contracts, net | [1] | 0 | 0
Interest rate derivatives | Other Noncurrent Liabilities |  |  |
Offsetting Liabilities [Line Items] |  |  |
Gross amounts of recognized liabilities |  | 0 | 6
Gross asset amounts offset in the Balance Sheet |  | 0 | 0
Liability derivative contracts, net |  | $ 0 | $ 6
[1] | The net amounts of derivative assets and liabilities are reconciled to the individual line item amounts presented in the unaudited Condensed Consolidated Balance Sheet in Note 9.

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