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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

X

- Definition

Derivative Asset Noncurrent Collateral Obligation To Return Cash Offset

+ References

No definition available.

+ Details

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Balance Type:	credit
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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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X

- 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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Balance Type:	debit
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X

- 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

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Details

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