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Financial Derivative Instruments - Offsetting of Derivative Liabilities (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Other Noncurrent Liabilities |  |  |
Offsetting Liabilities |  |  |
Liabilities derivative contracts, net |  | $ 12 | $ 21
Fuel derivatives | Prepaid expenses and other current assets |  |  |
Offsetting Liabilities |  |  |
Gross amounts of recognized liabilities |  | 0 | 50
Gross amounts offset in the Balance Sheet |  | 0 | (50)
Liabilities derivative contracts, net |  | 0 | 0
Interest rate derivatives | Accrued Liabilities |  |  |
Offsetting Liabilities |  |  |
Gross amounts of recognized liabilities |  | 2 | 1
Gross amounts offset in the Balance Sheet |  | 0 | 0
Liabilities derivative contracts, net |  | 2 | 1
Interest rate derivatives | Other Noncurrent Liabilities |  |  |
Offsetting Liabilities |  |  |
Gross amounts of recognized liabilities |  | 12 | 21
Gross amounts offset in the Balance Sheet |  | 0 | 0
Liabilities derivative contracts, net | [1] | $ 12 | $ 21
[1] | The net amounts of derivative assets and liabilities are reconciled to the individual line item amounts presented in the Consolidated Balance Sheet in Note 15.

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- Definition Net fair value of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected to be offset against a right to receive collateral. + References No definition available. + Details
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- Definition Fair value of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, not subject to a master netting arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313 + Details
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