Derivatives - Not Designated as Hedging Instruments (Details) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($) $ / MMBTU MMBbls Bcf	Dec. 31, 2017 USD ($) $ / MMBTU MMBbls Bcf
Oil (in barrels) \| Net sales
Outstanding commodity derivatives contracts not designated as hedging instruments
Unrealized gain (loss) on derivatives not designated as hedges \| $	$ (18)	$ (47)
Natural gas (in cubic feet) \| Net sales
Outstanding commodity derivatives contracts not designated as hedging instruments
Unrealized gain (loss) on derivatives not designated as hedges \| $	$ (1)	$ 1
Long position \| Oil (in barrels)
Outstanding commodity derivatives contracts not designated as hedging instruments
Derivative, Nonmonetary Notional Amount, Volume \| MMBbls	57	61
Price (in USD per Bbl or MMBTU) \| $ / MMBTU	58.64	57.38
Short position \| Natural gas (in cubic feet)
Outstanding commodity derivatives contracts not designated as hedging instruments
Derivative, Nonmonetary Notional Amount, Volume \| Bcf	63	47
Price (in USD per Bbl or MMBTU) \| $ / MMBTU	2.35	2.73

The forward price on the price risk forward or futures contract, such as a gas futures contract.

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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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.

+ Details

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- Definition

Nominal volume used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

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