Property, Plant and Equipment - Capitalized Exploratory Well Costs - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014 Green Canyon 469 Block [Member]	Sep. 30, 2014 Block WA-390-P, Offshore Western Australia [Member]	Sep. 30, 2014 Offshore Ghana [Member] Well	Sep. 30, 2014 Offshore Ghana [Member] Well	Sep. 30, 2014 Projects under planning and development [Member]	Oct. 31, 2014 Stampede [Member]	Sep. 30, 2014 Stampede [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Exploratory dry hole costs which were incurred and subsequently expensed	$ 61
Capitalized exploratory well costs charged to expense	236	169
Capitalized exploratory well costs that have been capitalized for period greater than one year	$ 1,737
Capitalized well costs			48.00%		21.00%	2.00%		29.00%
Working interest in the blocks							25.00%	25.00%
Number of consecutive successful exploration wells					7
Number of wells appraisal drilling plans					7
Number of wells appraisal drilling plans approved					4
Number of wells appraisal drilling plans in process					3
Number of appraisal wells completed				3