Disclosures About Fair Value Measurements (Company's Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative, Fair Value, Net	$ 225	$ (174)
Commodity Derivative Price Swap Contracts [Member] \| Derivative Asset Current [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Asset, Fair Value, Gross Asset	145	59
Derivative Asset, Fair Value, Gross Liability	(10)	(55)
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	135	4
Commodity Derivative Price Swap Contracts [Member] \| Derivative Asset Noncurrent [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Asset, Fair Value, Gross Asset	94	0
Derivative Asset, Fair Value, Gross Liability	(4)	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	90	0
Commodity Derivative Price Swap Contracts [Member] \| Derivative Liability Current [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Liability, Fair Value, Gross Liability	(10)	(137)
Derivative Liability, Fair Value, Gross Asset	10	55
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0	(82)
Commodity Derivative Price Swap Contracts [Member] \| Derivative Liability Noncurrent [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Liability, Fair Value, Gross Liability	(4)	(96)
Derivative Liability, Fair Value, Gross Asset	4	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0	(96)
Fair Value Inputs Level 1 [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative, Fair Value, Net	0	0
Fair Value Inputs Level 1 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Asset Current [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Fair Value Inputs Level 1 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Asset Noncurrent [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Fair Value Inputs Level 1 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Liability Current [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value Inputs Level 1 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Liability Noncurrent [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value Inputs Level 2 [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative, Fair Value, Net	225	(174)
Fair Value Inputs Level 2 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Asset Current [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Asset, Fair Value, Gross Asset	145	59
Fair Value Inputs Level 2 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Asset Noncurrent [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Asset, Fair Value, Gross Asset	94	0
Fair Value Inputs Level 2 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Liability Current [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Liability, Fair Value, Gross Liability	(10)	(137)
Fair Value Inputs Level 2 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Liability Noncurrent [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Liability, Fair Value, Gross Liability	(4)	(96)
Fair Value Inputs Level 3 [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative, Fair Value, Net	0	0
Fair Value Inputs Level 3 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Asset Current [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Fair Value Inputs Level 3 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Asset Noncurrent [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Fair Value Inputs Level 3 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Liability Current [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value Inputs Level 3 [Member] \| Commodity Derivative Price Swap Contracts [Member] \| Derivative Liability Noncurrent [Member]
Fair Value Of Derivatives Disclosure Information [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 0	$ 0

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226003-175313

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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624163-113959

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226000-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=64830801&loc=SL51823488-111719

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- Definition

Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226006-175313

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=d3e41678-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=64830801&loc=SL51823488-111719

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624163-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226000-175313

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- Definition

Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=d3e41678-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226006-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13495-108611

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Balance Type:	debit
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- Definition

Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

+ References

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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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