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Financial Derivative Instruments - Collateral by Balance Sheet Location (Details) - Fuel derivatives - USD ($) $ in Millions | Jun. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Prepaid expenses and other current assets |  |
Derivative [Line Items] |  |
Cash collateral deposits held from CP for fuel contracts - current | $ 123 | $ 15
Other Assets |  |
Derivative [Line Items] |  |
Cash collateral deposits held from CP for fuel contracts - non-current | 32 | 0
Accounts Payable |  |
Derivative [Line Items] |  |
Due To Third Parties For Settled Fuel Contracts | 0 | 29
Accounts And Other Receivables |  |
Derivative [Line Items] |  |
Receivable from third parties for settled fuel contracts - current | $ 17 | $ 0

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- Definition Amount due to third parties for settled fuel contracts as of the end of the period reported, recorded in Accrued liabilities on the balance sheet. + References No definition available. + Details
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- Definition Amount receivable from third parties for settled fuel contracts as of the end of the period reported, recorded in Accounts and other receivables on the balance sheet. + References No definition available. + Details
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- Definition Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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