Supplementary Oil And Gas Information (Costs Related To Unproved Properties) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition Costs, Cumulative	$ 4,343
Exploration Costs, Cumulative	137
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative, Total	4,480	$ 5,198
CurrentYear [member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition Costs, Cumulative	245
Exploration Costs, Cumulative	2
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative, Total	247
PriorYear [member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition Costs, Cumulative	104
Exploration Costs, Cumulative	5
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative, Total	109
Second Prior Year [member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition Costs, Cumulative	29
Exploration Costs, Cumulative	8
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative, Total	37
Third Prior Year and Previous [member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Acquisition Costs, Cumulative	3,965
Exploration Costs, Cumulative	122
Capitalized Costs of Unproved Properties Excluded from Amortization, Cumulative, Total	$ 4,087

The capitalized costs incurred (excluded from amortization), as of the date of the balance sheet, to purchase, lease or otherwise acquire an unproved property, including costs of lease bonuses and options to purchase or lease properties, the portion of costs applicable to minerals when land including mineral rights is purchased in fee, brokers' fees, recording fees, legal costs, and other costs incurred in acquiring properties.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-10.(c)(7)(ii))
-URI http://asc.fasb.org/extlink&oid=82851474&loc=d3e511914-122862

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The sum of the capitalized costs incurred, as of the balance sheet date, of unproved properties excluded from amortization including acquisition costs, exploration costs, development costs, and production costs.

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The capitalized costs incurred (excluded from amortization), as of the date of the balance sheet, in identifying areas that may warrant examination and in examining specific areas that are considered to have prospects of containing oil and gas reserves, including costs of drilling exploratory wells and exploratory-type stratigraphic test wells. Exploration costs may be incurred both before acquiring the related property (sometimes referred to in part as prospecting costs) and after acquiring the property. Principal types of exploration costs, which include depreciation and applicable operating costs of support equipment and facilities and other costs of exploration activities, are: costs of topographical, geographical and geophysical studies, rights of access to properties to conduct those studies, and salaries and other expenses of geologists, geophysical crews, and others conducting those studies. Collectively, these are sometimes referred to as geological and geophysical or "G&G" costs. Exploration costs also include costs of carrying and retaining undeveloped properties, such as delay rentals, ad valorem taxes on properties, legal costs for title defense, the maintenance of land and lease records, dry hole contributions and bottom hole contributions, costs of drilling and equipping exploratory wells and costs of drilling exploratory-type stratigraphic test wells.

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