Debt and Interest Expense - Outstanding Debt Table (Detail) (USD $)	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Principal	$ 15,841,000,000				$ 16,952,000,000
Net unamortized discounts and premiums	(1,700,000,000)	[1]			(1,722,000,000)	[1]
Total borrowings	14,141,000,000		14,832,000,000	15,386,000,000	15,230,000,000
Less: Current portion of long-term debt	1,039,000,000				170,000,000
Total long-term debt	13,102,000,000				15,060,000,000
Western Gas Partners Limited Partnership [Member]
Debt Instrument [Line Items]
Principal	1,020,000,000				500,000,000
Long-term notes and debentures [Member]
Debt Instrument [Line Items]
Principal	$ 14,821,000,000				$ 16,452,000,000

[1] Unamortized discounts and premiums are amortized over the term of the related debt.