Acquisitions, Divestitures, and Assets Held for Sale - Acquisitions (Detail) - USD ($) shares in Millions, $ in Millions		1 Months Ended	12 Months Ended
	Dec. 15, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Purchase price			$ (25)	$ 1,740	$ 3
Issuance of common stock during the period		40.5	0.0	41.0	0.0
GOM Acquisition [Member]
Business Acquisition [Line Items]
Purchase price	$ 1,800
Anadarko's ownership in the Lucius development			49.00%
Current assets	8
Properties and equipment	2,492
Other assets	145
AROs	(816)
Net assets acquired	1,829
Accounts payable	5
Other long-term liabilities	109
Cash paid	1,715
Proportionate amount of gross proceeds paid from a certain contract	150
Revenues				$ 8,849	$ 9,786
Net income (loss)				$ (2,623)	$ (6,560)
GOM Acquisition [Member] | Fair Value, Inputs, Level 3 [Member] | Income Approach Valuation Technique [Member]
Business Acquisition [Line Items]
Fair Value of the contingent consideration	$ 103