Debt and Interest Expense - Debt Activity Table (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended										6 Months Ended	3 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2012 Revolving Credit Facility [Member]	Jun. 30, 2012 Revolving Credit Facility [Member]	Jun. 30, 2012 Revolving Credit Facility [Member] Western Gas Partners Limited Partnership [Member]	Mar. 31, 2012 Revolving Credit Facility [Member] Western Gas Partners Limited Partnership [Member]	Jun. 30, 2012 Revolving Credit Facility [Member] Western Gas Partners Limited Partnership [Member] Borrowings [Member]	Mar. 31, 2012 Revolving Credit Facility [Member] Western Gas Partners Limited Partnership [Member] Borrowings [Member]	Mar. 31, 2012 Senior Notes, 6 Point 125 Percent, Due 2012 [Member]	Jun. 30, 2012 Senior Notes, 4 Point 00 Percent, Due 2022 [Member] Western Gas Partners Limited Partnership [Member]	Jun. 30, 2012 Senior Notes, 4 Point 00 Percent, Due 2022 [Member] Western Gas Partners Limited Partnership [Member] Issuance Of Debt [Member]
Debt Instrument [Line Items]
Carrying value, beginning balance	$ 14,832	$ 15,386	$ 15,230
Issuances and Borrowings								55	319			516
Repayments				(700)	(800)	(334)	(40)			(131)
Other, net	9	9	8
Carrying value, ending balance	$ 14,141	$ 14,832	$ 15,386
Debt instrument, stated interest rate										6.125%	4.00%
Debt instrument, maturity date										Mar. 15, 2012	Jul. 01, 2022