Additional Financial Statement Information - Additional Income Statement Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Revenue
Revenue from Sales	$ 4,438	$ 4,986	$ 4,256
Production Expense
Lease Operating Expense	532
Lease Operating Expense		576	571
Production and Ad Valorem Taxes	175	190	118
Gathering, Transportation and Processing Expense	417	393	432
Other Royalty Expense	13	38	20
Total Production Expense	1,137	1,197	1,141
Exploration Expense
Leasehold Impairment and Amortization	0	1	62
Dry Hole Cost	100	1	9
Seismic, Geological and Geophysical	21	22	27
Staff Expense	48	54	55
Other	33	51	35
Total	202	129	188
Loss on Marcellus Shale Upstream Divestiture and Other
Loss on Sale	0	0	2,270
Exit Cost	0	0	93
Other	0	0	16
Total	0	0	(2,379)
Other Operating Expense, Net
Marketing Expense	34	40	47
Firm Transportation Exit Cost	88	0	0
Clayton Williams Energy Acquisition Expenses	0	0	100
Loss (Gain) on Asset Retirement Obligation Revisions	9	(25)	(42)
Other, Net	83	35	33
Total	214	50	138
Income from Equity Method Investments and Other
Other Revenue
Revenue from Sales	51	172	177
Midstream Services Revenues - Third Party
Other Revenue
Revenue from Sales	94	78	19
Other Revenue
Other Revenue
Revenue from Sales	$ 145	$ 250	$ 196