Acquisitions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended			12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	May 31, 2011	Dec. 31, 2012 Wattenberg Natural-Gas Processing Plant [Member]	Dec. 31, 2011 Wattenberg Natural-Gas Processing Plant [Member]	May 31, 2011 Wattenberg Natural-Gas Processing Plant [Member]	May 31, 2011 Wattenberg Natural-Gas Processing Plant [Member] Oil and Gas Exploration and Production Reporting Segment [Member]	Dec. 31, 2012 Platte Valley Natural-Gas Processing Plant and Related Gathering Systems [Member] Western Gas Partners Limited Partnership [Member]	Feb. 28, 2011 Platte Valley Natural-Gas Processing Plant and Related Gathering Systems [Member] Western Gas Partners Limited Partnership [Member]
Business Acquisition [Line Items]
Date of acquisition agreement				May 31, 2011				Feb. 28, 2011
Ownership interest acquired						93.00%
Business acquisition, cost of acquired entity, purchase price			$ 878			$ 576			$ 302
Ownership interest						100.00%
Business acquisition, purchase price allocation, goodwill			362				335
Business acquisition, purchase price allocation, amortizable goodwill for tax purposes						469
Loss on Anadarko's preexisting contracts with the previous Wattenberg Plant owner			76		76
Gain from the acquisition-date fair-value remeasurement of Anadarko's pre-acquisition 7% equity interest in the Wattenberg Plant					21
Pre-acquisition equity interest in the Wattenberg Plant						7.00%
Amounts of revenue and earnings that would have been recognized had the acquisitions occurred on January 1, 2011
Amounts of revenue and earnings that would have been recognized had the acquisitions occurred on January 1, 2010