Derivative and Financial Instruments - Commodity Balance Sheet (Details) - Commodity Contract [Member] - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative assets	$ 250	$ 410
Other assets [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative assets	30	40
Other accruals [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative liabilities	258	370
Other liabilities and deferred credits [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative liabilities	$ 23	$ 30

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

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- Definition

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+ References

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