Summary of Significant Accounting Policies (Detail) - USD ($) $ in Millions			3 Months Ended			9 Months Ended
	Jan. 01, 2016	Dec. 31, 2015	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Schedule Of Significant Accounting Policies [Line Items]
Asset impairment charges and unproved oil and gas leasehold impairments			$ 951			$ 1,200	$ 6,800
Asset impairments							6,300
U.K. Petroleum Revenue Tax rate	0.00%	35.00%
Impairment charge of PRT benefits, before tax						481
Impairment charge of PRT benefits, net of tax						289
Remaining recoverable PRT benefits			13			13
Oil and gas property, fair value disclosure			163	$ 143	$ 1,900	163	1,900	$ 516	$ 1,200
Impairment of goodwill							163
Impairment of equity method investment							148
Impairment of inventory							9
Oil and Gas Properties, Proved [Member]
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments			355		3,536	423	5,797
Oil and Gas Properties, Unproved [Member]
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments			114		$ 199	222	515
Gas Gathering, Transmission, and Processing Assets [Member]
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments				$ 105			$ 210
US and Canada [Member]
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments			470			645
Fair Value, Inputs, Level 3 [Member] | Gas Gathering, Transmission, and Processing Assets [Member]
Schedule Of Significant Accounting Policies [Line Items]
Property, plant and equipment, fair value			$ 175			$ 175