Additional Financial Statement Information - Additional Income Statement Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Sales of Purchased Oil and Gas and Other
Revenue from Sales	$ 4,986	$ 4,256	$ 3,491
Sales of Purchased Oil and Gas and Other
Lease Operating Expense	576	571	542
Production and Ad Valorem Taxes	190	118	57
Gathering, Transportation and Processing Expense	393	432	480
Total	1,197	1,141	1,100
Exploration Expense
Leasehold Impairment and Amortization	1	62	148
Dry Hole Cost	1	9	579
Seismic, Geological and Geophysical	22	27	76
Staff Expense	54	55	77
Other	51	35	45
Total	129	188	925
Loss on Marcellus Shale Upstream Divestiture and Other
Loss on Sale	0	2,270	0
Exit Cost	0	93	0
Other	0	16	0
Total	0	2,379	0
Other Operating Expense, Net
Marketing Expense	40	47	58
Cost of Purchased Oil and Gas	296	0	0
Gain on Divestitures, Net	0	100	0
Gain on Asset Retirement Obligation Revisions	(25)	(42)	0
Other, Net	35	33	77
Total	346	138	135
Purchased Oil and Gas
Sales of Purchased Oil and Gas and Other
Revenue from Sales	275	0	0
Sales of Purchased Oil and Gas and Other
Cost of Goods and Services Sold	296
Income from Equity Method Investees
Sales of Purchased Oil and Gas and Other
Revenue from Sales	172	177	102
Midstream Services Revenues - Third Party
Sales of Purchased Oil and Gas and Other
Revenue from Sales	78	19	0
Sales of Purchased Oil and Gas and Other
Sales of Purchased Oil and Gas and Other
Revenue from Sales	525	196	102
Other Royalty Expense
Sales of Purchased Oil and Gas and Other
Cost of Goods and Services Sold	$ 38	$ 20	$ 21