Noncontrolling Interests (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Noncontrolling Interest [Line Items]
Net proceeds raised from offering by subsidiary	$ 623	$ 328	$ 338
Western Gas Equity Partners Limited Partnership [Member]
Noncontrolling Interest [Line Items]
Net proceeds raised from initial public offering by subsidiary	411
Western Gas Equity Partners Limited Partnership [Member] | Limited Partner [Member]
Noncontrolling Interest [Line Items]
Ownership interest in subsidiary	91.00%
Western Gas Equity Partners Limited Partnership [Member] | IPO [Member]
Noncontrolling Interest [Line Items]
Common units issued to the public	20
Issuance price per common unit	$ 22.00
Western Gas Partners Limited Partnership [Member]
Noncontrolling Interest [Line Items]
Common units issued to the public	5	10	13
Net proceeds raised from offering by subsidiary	$ 212	$ 328	$ 338
Western Gas Partners Limited Partnership [Member] | Limited Partner [Member]
Noncontrolling Interest [Line Items]
Ownership interest in subsidiary	46.20%
Western Gas Partners Limited Partnership [Member] | General Partner [Member]
Noncontrolling Interest [Line Items]
Ownership interest in subsidiary	2.00%