Acquisitions and Divestitures Acquisitions and Divestitures (Acquisitions Narrative) (Details) - USD ($) shares in Millions, $ in Millions	1 Months Ended				12 Months Ended
	Jul. 31, 2020	May 31, 2019	Dec. 31, 2018	Aug. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Proceeds from disposition of assets, net of cash sold					$ 60	$ 149	$ 469
Payments for undeveloped acreage					14	28	65
Disposal Group, Contingent Consideration Received	$ 49
Total consideration						56
Gain (Loss) on Disposition of Property Plant Equipment					9	(477)	290
Increase (Decrease) In Deficiency Fee Receivable					(4)
Restricted Cash					75
South Texas Divestiture
Business Acquisition [Line Items]
Proceeds from disposition of assets, net of cash sold		$ 2
Guarantor Obligations, Reimbursement					$ 75
Total consideration		210
Contingent Consideration		136
Gain (Loss) on Disposition of Property Plant Equipment						525
West Panhandle
Business Acquisition [Line Items]
Proceeds from disposition of assets, net of cash sold				$ 170
Employee-related charges				7
Gain (Loss) on Disposition of Property Plant Equipment				$ 127
Pressure pumping assets | Sale assets
Business Acquisition [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment							30
Pressure pumping assets | ProPetro | Sale assets
Business Acquisition [Line Items]
Employee-related charges						$ 1	19
Total consideration			$ 282				282
Shares received			16.6
ProPetro
Business Acquisition [Line Items]
Investment in affiliate			$ 172				$ 172
South Texas Divestiture | South Texas Divestiture
Business Acquisition [Line Items]
Guarantor Obligations, Reimbursement		$ 72