Debt Activity Table (Detail) (USD $) In Millions, unless otherwise specified					3 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Jun. 30, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Principal Amount [Member] Senior Notes, 5 Point 375 Percent, Due 2021 [Member]	Mar. 31, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Principal Amount [Member] Credit facility and term loan [Member]		Sep. 30, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Principal Amount [Member] Credit facility [Member]		Jun. 30, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Principal Amount [Member] Credit facility [Member]		Mar. 31, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Principal Amount [Member] Credit facility [Member]	Sep. 30, 2011 Debt Outstanding Principal Amount [Member] Senior Notes, 6 Point 875 Percent, Due 2011 [Member]		Jun. 30, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Carrying Amount [Member] Senior Notes, 5 Point 375 Percent, Due 2021 [Member]	Mar. 31, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Carrying Amount [Member] Credit facility and term loan [Member]		Sep. 30, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Carrying Amount [Member] Credit facility [Member]		Jun. 30, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Carrying Amount [Member] Credit facility [Member]		Mar. 31, 2011 Western Gas Partners Limited Partnership [Member] Debt Outstanding Carrying Amount [Member] Credit facility [Member]	Sep. 30, 2011 Debt Outstanding Carrying Amount [Member]	Jun. 30, 2011 Debt Outstanding Carrying Amount [Member]	Mar. 31, 2011 Debt Outstanding Carrying Amount [Member]	Sep. 30, 2011 Debt Outstanding Carrying Amount [Member] Senior Notes, 6 Point 875 Percent, Due 2011 [Member]		Sep. 30, 2011 Western Gas Partners Limited Partnership [Member] Long-term debt [Member]	Dec. 31, 2010 Western Gas Partners Limited Partnership [Member] Long-term debt [Member]	Sep. 30, 2011 Long-term debt [Member]	Jun. 30, 2011 Long-term debt [Member]	Mar. 31, 2011 Long-term debt [Member]	Dec. 31, 2010 Long-term debt [Member]	Jun. 30, 2011 Western Gas Partners Limited Partnership [Member] Senior Notes, 5 Point 375 Percent, Due 2021 [Member]	Sep. 30, 2011 Senior Notes, 6 Point 875 Percent, Due 2011 [Member]	Sep. 30, 2011 Western Gas Partners Limited Partnership [Member]	Dec. 31, 2010 Western Gas Partners Limited Partnership [Member]
Debt Instrument [Line Items]
Principal amount, beginning balance																												$ 500	$ 299	$ 14,452	$ 14,737	$ 14,707	$ 14,536
Carrying amount, beginning balance	12,720	12,998	12,966	12,787																																494	299
Issuance					500										494
Borrowings								10				560						10				560
Repayments						(389)	[1]	(10)	[1]	(470)	[1]		(285)	[1]		(389)	[1]	(10)	[1]	(470)	[1]					(285)	[1]
Other, net																							7	8	8
Principal amount, ending balance																												500	299	14,452	14,737	14,707	14,536
Carrying amount, ending balance	$ 12,720	$ 12,998	$ 12,966	$ 12,787																																$ 494	$ 299
Debt instrument, interest rate, stated percentage																																		5.375%	6.875%

[1] Debt repayment activity includes both scheduled repayments and retirements before scheduled maturity.