Supplemental Information On Oil And Natural Gas Producing Activities (Proved Reserves) (Details) - MMBoe	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Changes in proved developed and undeveloped reserves
Balance	6,870	11,642
Purchase of reserves in place		1,397
Sales of reserves in place	(1,731)	(610)
Revisions of previous estimates	1,062	(4,426)
Production	(936)	(1,133)
Balance	5,265	6,870
Proved developed reserves	5,265	6,870
Oil
Changes in proved developed and undeveloped reserves
Balance	3,514	3,159
Purchase of reserves in place		1,049
Sales of reserves in place	(358)	(47)
Revisions of previous estimates	504	(316)
Production	(414)	(331)
Balance	3,246	3,514
Proved developed reserves	3,246	3,514
Natural Gas
Changes in proved developed and undeveloped reserves
Balance	2,426	7,736
Purchase of reserves in place		176
Sales of reserves in place	(1,280)	(563)
Revisions of previous estimates	383	(4,202)
Production	(420)	(721)
Balance	1,109	2,426
Proved developed reserves	1,109	2,426
Natural Gas Liquids
Changes in proved developed and undeveloped reserves
Balance	930	747
Purchase of reserves in place		172
Sales of reserves in place	(93)
Revisions of previous estimates	175	92
Production	(102)	(81)
Balance	910	930
Proved developed reserves	910	930

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Energy measure of proved reserve of oil and gas, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

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- Definition

Energy measure of decrease in quantity of proved reserve of oil and gas resulting from production, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

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Energy measure of increase in quantity of proved reserve of oil and gas resulting from purchase of mineral in place, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

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- Definition

Energy measure of increase (decrease) in quantity of proved reserve of oil and gas related to revision of a previous estimate resulting from new information, except for an increase in proved acreage, or change in economic factors, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

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- Definition

Energy measure of decrease in quantity of proved reserve of oil and gas resulting from sale of mineral in place, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

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- Definition

Energy measure of interests in proved developed reserves of crude oil, including condensate and natural gas liquids, natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas.

+ References

No definition available.

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