Divestitures (Narrative) (Details) - USD ($)			1 Months Ended			3 Months Ended		12 Months Ended			24 Months Ended
	Dec. 03, 2018	Aug. 30, 2018	Dec. 31, 2018	Sep. 30, 2018	Jul. 31, 2016	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments								$ 171,000,000		$ 2,321,000,000
Gain on the sale of non-full cost pool assets	$ 17,000,000
Reduction of full cost pool assets	887,000,000
Gain on sale of assets, net								(17,000,000)	$ (6,000,000)
Repayments of long-term debt								2,095,000,000	1,139,000,000	1,175,000,000
Cash paid for interest								135,000,000	$ 130,000,000	$ 75,000,000
Treasury stock acquired						$ 155,000,000	$ 25,000,000	$ 180,000,000
Treasury stock, shares								39,061,269
Discontinued Operations, Held-for-sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments							160,000,000	$ 160,000,000
Fayetteville Shale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest prior to disposal		100.00%		100.00%
Consideration		$ 1,865,000,000		$ 1,865,000,000			1,865,000,000
Proceeds from sale of oil and gas property and equipment	1,650,000,000
Adjustment due to differences from economic effective date to close date	215,000,000
Derivative liabilities	$ 151,000,000
Gain on sale of assets, net								22,000,000
Contractual commitments assumed by buyer			$ 221,000,000			221,000,000		221,000,000
Liability for estimated future payments			88,000,000			$ 88,000,000		88,000,000
Other Non-Core Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments								11,000,000
Scenario, Forecast [Member] | Fayetteville Shale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Potential amount to be reimbursed to buyer											$ 102,000,000
Midstream Services [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments								155,000,000
Gain on sale of assets, net								(35,000,000)
Midstream Services [Member] | Discontinued Operations, Held-for-sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments							145,000,000	145,000,000
Exploration and Production [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments								15,000,000
Gain on sale of assets, net								18,000,000
Exploration and Production [Member] | Discontinued Operations, Held-for-sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments							$ 15,000,000	15,000,000
Other [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments								$ 1,000,000
Senior Notes [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayment of debt			914,000,000
Repayments of long-term debt			900,000,000		$ 700,000,000
Cash paid for interest			$ 9,000,000