Divestitures (Details) - USD ($) $ in Millions			1 Months Ended		3 Months Ended			6 Months Ended	9 Months Ended
	Dec. 03, 2018	Aug. 30, 2018	Jul. 31, 2019	Dec. 31, 2018	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contractual commitments assumed by buyer					$ 135				$ 135
Potential amount to be reimbursed to buyer					70				70
Liability for estimated future payments				$ 88	57			$ 88	57
Impairments					2		$ 161		8	$ 171
Repayments of long-term debt									43	1,191
Treasury stock acquired				201		$ 21	25	$ 180
Commissions				$ 1
Treasury stock acquired (in shares)				44,000,000		5,260,687		39,061,269
Non-Core Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments							1			1
Midstream
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments					2		145		2	155
E&P
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments					0		15		$ 6	15
Fayetteville Shale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest prior to disposal		100.00%
Consideration		$ 1,865
Proceeds from disposal	$ 1,650
Adjustment due to differences from economic effective date to close date	$ 215
Impairments							161			161
Fayetteville Shale | Midstream
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments							145			145
Fayetteville Shale | E&P
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments							$ 15			$ 15
Non-core leasehold
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration											$ 25
Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration			$ 16
Gain on disposal			$ 2
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	$ 43
Cash paid for interest				$ 9