Asset Impairments (Summary of Asset Impairments) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Impaired Long Lived Assets Held And Used [Line Items]
Asset impairment charges	$ 2,693		$ 156
Unproved impairments	167	$ 58	128
Proved Oil and Gas Assets [Member]
Impaired Long Lived Assets Held And Used [Line Items]
Asset impairment charges	2,664		109
Other Assets [Member]
Impaired Long Lived Assets Held And Used [Line Items]
Asset impairment charges	29		47
Unproved Impairments [Member]
Impaired Long Lived Assets Held And Used [Line Items]
Unproved impairments	$ 152	$ 18	$ 95

Exploration expenses (including prospecting) related to oil and gas producing entities and would be included in operating expenses of that entity. Costs incurred 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: (i) 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. (ii) Costs of carrying and retaining undeveloped properties, such as delay rentals, ad valorem taxes on properties, legal costs for title defense, and the maintenance of land and lease records. (iii) Dry hole contributions and bottom hole contributions. (iv) Costs of drilling and equipping exploratory wells. (v) Costs of drilling exploratory-type stratigraphic test wells.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 23
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62136-109447

Name:	us-gaap_ExplorationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration