Supplemental Oil and Gas Disclosures (Capitalized Costs Relating to Oil and Gas Producing Activities Disclosure) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Supplemental Oil and Gas Disclosures [Abstract]
Proved properties	$ 22,425	$ 22,073
Unproved properties	1,755	1,817
Total capitalized costs	24,180	23,890
Less: Accumulated depreciation, depletion and amortization	(19,761)	(19,287)
Net capitalized costs	$ 4,419	$ 4,603

Amount of accumulated depreciation, depletion, amortization and valuation allowance relating to oil and gas producing activities.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 235
-Section 50
-Paragraph 13
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The sum of capitalized costs relating to oil and gas producing activities before accounting for accumulated depreciation.

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Net amount of capitalized costs relating to oil and gas producing activities.

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Capitalized costs of proved properties incurred for any combination mineral interests acquisitions; wells and related equipment; support equipment and facilities; and uncompleted wells and equipment and other costs not previously disclosed within this table.

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Capitalized costs of unproved properties incurred for any combination mineral interests acquisitions and other costs not previously disclosed within this table.

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-Publisher FASB
-Name Accounting Standards Codification
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