Divestitures (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended			6 Months Ended	12 Months Ended
	Jul. 31, 2019	Dec. 31, 2018	Aug. 31, 2018	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 03, 2018	Aug. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
(Gain) loss on sale of operating assets, net									$ 2	$ (17)	$ (6)
Contractual commitments assumed by buyer							$ 108		108
Potential amount to be reimbursed to buyer									58
Liability for estimated future payments		$ 88			$ 88		46		46	88
Impairments									16	171	0
Cash paid for interest									58	135	130
Treasury stock acquired		$ 201		$ 21	$ 180				$ 21	$ 180
Treasury stock (in shares)		44,000,000		5,260,687	39,061,268				5,260,687	39,061,268
Payments for commissions		$ 1
Proceeds from sale of property and equipment									$ 54	$ 1,643	$ 10
Discontinued operations, held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments						$ 161				160
Fayetteville Shale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest prior to disposal			100.00%
Disposal Group, Including Discontinued Operation, Consideration													$ 1,865
Proceeds from sale of oil and gas property and equipment		1,650
Adjustment due to differences from economic effective date to close date		215
Gain on the sale of non-full cost pool assets		17
Reduction of full cost pool assets		887
Derivative liabilities												$ 151
(Gain) loss on sale of operating assets, net										22
Contractual commitments assumed by buyer							108		108
Liability for estimated future payments							46		46
Fayetteville Shale | Forecast
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Potential amount to be reimbursed to buyer								$ 58
Other non-core assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments						1			16	11
Proceeds from sale of property and equipment									$ 38
Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
(Gain) loss on sale of operating assets, net	$ (2)
Proceeds from sale of property and equipment	$ 16
Senior Notes
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayment of debt		914
Repayments of long-term debt		900					$ 54
Cash paid for interest		$ 9
Marketing | Discontinued operations, held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments						145				145
Exploration and Production | Discontinued operations, held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments						$ 15				$ 15