Divestitures - Divestitures (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from divestitures			$ 393	$ 3,480
Gain (loss) on divestitures			31	815	[1]
Exploration and Production [Member] | Certain Onshore Domestic Assets Ram Powell [Member] | Asset Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on divestitures			67
Exploration and Production [Member] | Certain U.S. Onshore Assets in Eagleford, South Texas [Member] | Asset Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from divestitures				2,100
Gain (loss) on divestitures				730
Exploration and Production [Member] | Certain Onshore Domestic Assets, Eaglebine, Southeast Texas [Member] | Asset Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from divestitures				533
Gain (loss) on divestitures				282
Exploration And Production And Other Midstream Reporting Segment [Member] | Certain Onshore Domestic Assets Alaska [Member] | Asset Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from divestitures			370
Gain (loss) on divestitures	$ (154)		$ (33)
Exploration And Production And Other Midstream Reporting Segment [Member] | Certain U.S. Onshore Assets in Marcellus, Pennsylvania [Member] | Asset Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from divestitures				758
Gain (loss) on divestitures		$ (129)		(56)
Exploration And Production And Other Midstream Reporting Segment [Member] | Certain Onshore Domestic Assets, CBM, Utah [Member] | Asset Disposed of by Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from divestitures				69
Gain (loss) on divestitures				$ (52)

[1] Includes the $126 million gain related to the 2017 property exchange discussed below.