Supplemental Information On Oil And Natural Gas Producing Activities (Proved Reserves Narrative) (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($) MMBoe $ / bbl $ / Mcf	Dec. 31, 2018 USD ($) MMBoe $ / bbl $ / Mcf	Dec. 31, 2017 MMBoe
Reserve Quantities [Line Items]
Exploration and dry hole costs \| $	$ 0.0	$ 0.0
Proved reserve estimates	2,999	3,453	5,265
Reserve revision	2,999	3,453
Increase (decrease) in proved reserve estimates	0.5
Production	(309)	(439)
Revisions of previous estimates	(145)	(268)
Oil reserves
Reserve Quantities [Line Items]
Proved reserve estimates	2,241	2,479	3,246
Reserve revision	2,241	2,479
Production	(228)	(296)
Revisions of previous estimates	(10)	(199)
Weighted-average product price \| $ / bbl	59.55	66.95
Natural gas
Reserve Quantities [Line Items]
Proved reserve estimates	348	454	1,109
Reserve revision	348	454
Production	(39)	(72)
Revisions of previous estimates	(67)	(261)
Weighted-average product price \| $ / Mcf	2.66	3.21
Natural gas liquids
Reserve Quantities [Line Items]
Proved reserve estimates	410	520	910
Reserve revision	410	520
Production	(42)	(71)
Revisions of previous estimates	(68)	192
Weighted-average product price \| $ / bbl	13.68	23.00
Louisiana, Briggs, and Cola Divestiture
Reserve Quantities [Line Items]
Increase (decrease) in proved reserve estimates		1.8	1.1

Proved Developed Reserves, Increase (Decrease)

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Weighted-Average Product Price

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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/disclosureRef
-Publisher SEC
-Name Form 20-F
-Section Item 18
-Subsection Instruction 2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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-SubTopic 235
-Section 50
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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/2009/role/commonPracticeRef
-Publisher SEC
-Name Form 20-F
-Section Item 18
-Subsection Instruction 2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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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/2009/role/commonPracticeRef
-Publisher SEC
-Name Form 20-F
-Section Item 18
-Subsection Instruction 2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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-Topic 932
-SubTopic 235
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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.

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- Definition

Dry hole costs from oil and gas producing activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
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