Noncontrolling Interests (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended			1 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Western Gas Equity Partners Limited Partnership [Member] Limited Partner [Member]	May 31, 2013 Western Gas Partners Limited Partnership [Member]	Jun. 30, 2013 Western Gas Partners Limited Partnership [Member] Limited Partner [Member] Western Gas Equity Partners Limited Partnership, Ownership Interest [Member]	Jun. 30, 2013 Western Gas Partners Limited Partnership [Member] Limited Partner [Member] Other Anadarko Subsidiary, Ownership Interest [Member]	Jun. 30, 2013 Western Gas Partners Limited Partnership [Member] General Partner [Member] Western Gas Equity Partners Limited Partnership, Ownership Interest [Member]
Noncontrolling Interest [Line Items]
Ownership interest in subsidiary			91.00%		43.10%	0.40%	2.00%
Common units issued to the public				7
Net proceeds raised from offering by subsidiary	$ 415	$ 212		$ 416