Divestitures (Details) - USD ($) $ in Millions			1 Months Ended	3 Months Ended	6 Months Ended
	Dec. 03, 2018	Aug. 30, 2018	Dec. 31, 2018	Mar. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contractual commitments assumed by buyer				$ 188
Potential amount to be reimbursed to buyer				94
Liability for estimated future payments			$ 88	78	$ 88
Treasury stock acquired			201	$ 21	$ 180
Commissions			$ 1
Treasury stock acquired (in shares)			44,000,000	5,260,687	39,061,269
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
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
Cash paid for interest			$ 9