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Acquisitions and Dispositions - Acquisition of Concho Resources Inc. (Concho) - Textual (Details) $ in Millions			3 Months Ended			9 Months Ended
	Feb. 08, 2021 USD ($)	Jan. 15, 2021 USD ($)	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Business Acquisition [Line Items]
Income tax provision			$ 1,203		$ (62)		$ 2,924	$ (171)
Total revenues and other income						$ 4,499
Net loss						(1,600)
Sales and other operating revenues [Member] \| Commodity Contract [Member]
Business Acquisition [Line Items]
Loss from commodity derivatives, before tax and after tax			483		(33)		862	(30)
Other Income (Loss) [Member] \| Commodity Contract [Member]
Business Acquisition [Line Items]
Loss from commodity derivatives, before tax and after tax			(7)		2		(23)	(3)
Purchased commodities [Member] \| Commodity Contract [Member]
Business Acquisition [Line Items]
Loss from commodity derivatives, before tax and after tax			(405)		27		$ (550)	29
Concho Resources Incorporated [Member]
Business Acquisition [Line Items]
Name of acquired entity							Concho Resources Inc.
Date of acquisition agreement							Jan. 15, 2021
Exchange ratio		1.46
Total Consideration		$ 13,125
Capitalized costs, proved properties		11,800
Capitalized costs, unproved properties		$ 6,900
Transaction Cost				$ 157			$ 157
Restructuring Cost			$ 52				209
Income tax provision	$ 75						$ 75
Total revenues and other income					5,019			16,384
Net loss					$ 565			1,184
Concho Resources Incorporated [Member] \| Concho Resources Inc. [Member]
Business Acquisition [Line Items]
Impairment of Oil and Gas Properties								10,500
Goodwill, impairment loss								$ 1,900
Concho Resources Incorporated [Member] \| Commodity Contract [Member]
Business Acquisition [Line Items]
Loss from commodity derivatives, before tax and after tax				305		233
Concho Resources Incorporated [Member] \| Sales and other operating revenues [Member] \| Commodity Contract [Member]
Business Acquisition [Line Items]
Loss from commodity derivatives, before tax and after tax				173		$ 305
Concho Resources Incorporated [Member] \| Sales and other operating revenues [Member] \| Accelerated contracts [Member]
Business Acquisition [Line Items]
Loss from commodity derivatives, before tax and after tax				$ 132