Restructuring Charges (Summary of Restructuring Charges Related to Workforce Reduction Plans) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 16	$ 11	$ 39
Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Severance (including payroll taxes)	16	0	21
Outplacement services, other	0	0	2
Total restructuring charges	16	$ 0	23
Workforce Reduction \| Exploration and Production
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 16		21
Workforce Reduction \| Marketing
Restructuring Cost and Reserve [Line Items]
Total restructuring charges			$ 2

Amount of other expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses associated with a discontinued operation or an asset retirement obligation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Data Type:	xbrli:monetaryItemType
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