Debt and Interest Expense - Outstanding Debt and Capital Lease Obligations Table (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Debt Instrument [Line Items]
Principal	$ 16,952		$ 14,536
Total borrowings	15,230		12,787		12,748
Net unamortized discounts and premiums	(1,722)	[1]	(1,749)	[1]
Capital lease obligation			226
Less: Current portion of long-term debt	170		291
Total long-term debt	15,060		12,722
Western Gas Partners Limited Partnership [Member]
Debt Instrument [Line Items]
Principal	500		299
Senior Notes, 6 Point 875 Percent, Due 2011 [Member]
Debt Instrument [Line Items]
Principal			285
Senior Notes, 6 Point 125 Percent, Due 2012 [Member]
Debt Instrument [Line Items]
Principal	131		131
Senior Notes, 5 Point 000 Percent, Due 2012 [Member]
Debt Instrument [Line Items]
Principal	39		39
Senior Notes, 5 Point 750 Percent, Due 2014 [Member]
Debt Instrument [Line Items]
Principal	275		275
Senior Notes, 7 Point 625 Percent, Due 2014 [Member]
Debt Instrument [Line Items]
Principal	500		500
Senior Notes, 5 Point 950 Percent, Due 2016 [Member]
Debt Instrument [Line Items]
Principal	1,750		1,750
Senior Notes, 6 Point 375 Percent, Due 2017 [Member]
Debt Instrument [Line Items]
Principal	2,000		2,000
Debentures, 7 Point 050 Percent, Due 2018 [Member]
Debt Instrument [Line Items]
Principal	114		114
Senior Notes, 6 Point 950 Percent, Due 2019 [Member]
Debt Instrument [Line Items]
Principal	300		300
Senior Notes, 8 Point 700 Percent, Due 2019 [Member]
Debt Instrument [Line Items]
Principal	600		600
Senior Notes, 6 Point 950 Percent, Due 2024 [Member]
Debt Instrument [Line Items]
Principal	650		650
Debentures, 7 Point 500 Percent, Due 2026 [Member]
Debt Instrument [Line Items]
Principal	112		112
Debentures, 7 Point 000 Percent, Due 2027 [Member]
Debt Instrument [Line Items]
Principal	54		54
Debentures, 7 Point 125 Percent, Due 2027 [Member]
Debt Instrument [Line Items]
Principal	150		150
Debentures, 6 Point 625 Percent Due 2028 [Member]
Debt Instrument [Line Items]
Principal	17		17
Debentures, 7 Point 150 Percent, Due 2028 [Member]
Debt Instrument [Line Items]
Principal	235		235
Debentures, 7 Point 200 Percent, Due 2029 [Member]
Debt Instrument [Line Items]
Principal	135		135
Debentures, 7 Point 950 Percent, Due 2029 [Member]
Debt Instrument [Line Items]
Principal	117		117
Senior Notes, 7 Point 500 Percent, Due 2031 [Member]
Debt Instrument [Line Items]
Principal	900		900
Senior Notes, 7 Point 875 Percent, Due 2031 [Member]
Debt Instrument [Line Items]
Principal	500		500
Senior Notes, Zero Coupon Maturing October 2036 [Member]
Debt Instrument [Line Items]
Principal	2,360		2,360
Senior Notes, 6 Point 450 Percent, Due 2036 [Member]
Debt Instrument [Line Items]
Principal	1,750		1,750
Senior Notes, 7 Point 950 Percent, Due 2039 [Member]
Debt Instrument [Line Items]
Principal	325		325
Senior Notes, 6 Point 200 Percent, Due 2040 [Member]
Debt Instrument [Line Items]
Principal	750		750
Debentures, 7 Point 730 Percent, Due 2096 [Member]
Debt Instrument [Line Items]
Principal	61		61
Debentures, 7 Point 500 Percent, Due 2096 [Member]
Debt Instrument [Line Items]
Principal	78		78
Debentures, 7 Point 250 Percent, Due 2096 [Member]
Debt Instrument [Line Items]
Principal	49		49
Five Billion Dollar Facility [Member]
Debt Instrument [Line Items]
Principal	$ 2,500

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