Divestitures - Divestitures and Assets Held for Sale (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017		Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from divestitures	$ 371		$ 2,851
Gain (loss) on divestitures	24		(804)	[1]
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			(726)
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	383
Gain (loss) on divestitures	$ (30)	$ (154)
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			763
Gain (loss) on divestitures			$ (44)		$ (129)

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