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Financial Derivative Instruments - Collateral by Balance Sheet Location (Details) - Fuel derivatives - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value	$ 15
Prepaid expenses and other current assets
Derivative [Line Items]
Total Collateral Already Received Aggregate Fair Value	15	$ 4
Other Assets
Derivative [Line Items]
Total Collateral Already Received Aggregate Fair Value	0	6
Accounts Payable
Derivative [Line Items]
Due To Third Parties For Settled Fuel Contracts	29	75
Accrued Liabilities
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value	$ 0	$ 311

X

- 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

Total cash, current and noncurrent, that is already received, at the end of the reporting period, as collateral for derivative instruments.

+ References

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- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

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- Definition

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+ References

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