ACQUISITIONS AND DIVESTITURES - Assets Acquired and Liabilities Assumed as of Acquisition Date (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Business Acquisition [Line Items]
Proved properties	$ 74,743		$ 67,805
Unproved properties	9,196		5,530
Mobil North Sea Limited [Member]
Business Acquisition [Line Items]
Current assets	208
Proved properties	2,341
Unproved properties	476
Gathering, transmission and processing facilities	338
Goodwill	82	[1]
Total assets acquired	3,445
Current liabilities	148
Asset retirement obligation	517
Deferred income tax liabilities	1,533
Non-current obligations	1
Total liabilities assumed	2,199
Net assets acquired	1,246
Cordillera Energy Partners [Member]
Business Acquisition [Line Items]
Current assets	56
Proved properties	1,040
Unproved properties	2,288
Gathering, transmission and processing facilities	1
Total assets acquired	3,385
Current liabilities	86
Non-current obligations	5
Total liabilities assumed	91
Net assets acquired	$ 3,294

[1] Goodwill was the excess of the consideration transferred over the net assets recognized and represents the future economic benefits arising from assets acquired that could not be individually identified and separately recognized. Goodwill is not deductible for tax purposes.