Selected Financial Information for Anadarko's Reporting Segments Table (Detail) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Segment Reporting Information [Line Items]
Sales revenues	$ 3,384		$ 2,516		$ 10,342		$ 8,209
Gains (losses) on divestitures and other, net	(185)		34		(214)		84
Total revenues and other	3,199		2,550		10,128		8,293
Operating costs and expenses	1,361	[1]	1,074	[1]	3,891	[2]	3,158	[2]
Other (income) expense, net	40		(129)		(2)		(106)
Net income attributable to noncontrolling interests	23		18		62		42
Total expenses and other	1,353		806		3,798		2,755
Unrealized (gains) losses on derivatives, net					767		(66)
Adjusted EBITDAX	1,843		1,740		6,322		5,529
Oil and Gas Exploration and Production Reporting Segment [Member]
Segment Reporting Information [Line Items]
Sales revenues	1,801		1,318		5,668		4,117
Intersegment revenues	1,244		950		3,699		3,259
Gains (losses) on divestitures and other, net	(193)		(3)		(307)		(15)
Total revenues and other	2,852		2,265		9,060		7,361
Operating costs and expenses	955	[1]	723	[1]	2,739	[2]	2,169	[2]
Total expenses and other	955		723		2,739		2,169
Adjusted EBITDAX	1,897		1,542		6,321		5,192
Midstream Reporting Segment [Member]
Segment Reporting Information [Line Items]
Sales revenues	76		45		238		145
Intersegment revenues	251		198		684		630
Gains (losses) on divestitures and other, net	(31)				(11)
Total revenues and other	296		243		911		775
Operating costs and expenses	210	[1]	152	[1]	575	[2]	501	[2]
Net income attributable to noncontrolling interests	23		18		62		42
Total expenses and other	233		170		637		543
Adjusted EBITDAX	63		73		274		232
Commodity Contract [Member] | Nondesignated [Member] | Gathering, Processing, and Marketing Sales [Member] | Marketing Reporting Segment [Member]
Segment Reporting Information [Line Items]
Unrealized (gains) losses on derivatives, net	(3)		(4)		(8)		(9)
Marketing Reporting Segment [Member]
Segment Reporting Information [Line Items]
Sales revenues	1,507		1,153		4,436		3,947
Intersegment revenues	(1,386)		(1,051)		(4,066)		(3,593)
Total revenues and other	121		102		370		354
Operating costs and expenses	143	[1]	116	[1]	414	[2]	349	[2]
Total expenses and other	143		116		414		349
Adjusted EBITDAX	(25)		(18)		(52)		(4)
Nondesignated [Member] | Other and Intersegment Eliminations [Member] | (Gains) Losses on Commodity Derivatives, Net and (Gains) Losses on Other Derivatives, Net [Member] | Commodity Contract, Interest Rate Contract, and Other [Member]
Segment Reporting Information [Line Items]
Realized (gains) losses on derivatives, net	(71)		(157)		(153)		(339)
Other and Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment revenues	(109)		(97)		(317)		(296)
Gains (losses) on divestitures and other, net	39		37		104		99
Total revenues and other	(70)		(60)		(213)		(197)
Operating costs and expenses	53	[1]	83	[1]	163	[2]	139	[2]
Other (income) expense, net	40		(129)		(2)		(106)
Total expenses and other	22		(203)		8		(306)
Adjusted EBITDAX	(92)		143		(221)		109
Commodity Contract [Member] | Nondesignated [Member] | Gathering, Processing, and Marketing Sales [Member]
Segment Reporting Information [Line Items]
Realized (gains) losses on derivatives, net	1	[3]			17	[3]	1	[3]
Unrealized (gains) losses on derivatives, net	(3)	[3]	(4)	[3]	(8)	[3]	(9)	[3]
Nondesignated [Member] | (Gains) Losses on Commodity Derivatives, Net and (Gains) Losses on Other Derivatives, Net [Member] | Commodity Contract, Interest Rate Contract, and Other [Member]
Segment Reporting Information [Line Items]
Realized (gains) losses on derivatives, net	(71)		(157)		(153)		(339)
Nondesignated [Member]
Segment Reporting Information [Line Items]
Realized (gains) losses on derivatives, net	(70)		(157)		(136)		(338)
Unrealized (gains) losses on derivatives, net	692	[4]	174	[4]	767	[4]	(66)	[4]
Restatement Adjustment [Member] | Oil and Gas Exploration and Production Reporting Segment to Midstream Reporting Segment [Member]
Segment Reporting Information [Line Items]
Adjustment amount			$ 25				$ 57

[1] Operating costs and expenses exclude exploration expense; depreciation, depletion, and amortization; impairments; and Deepwater Horizon settlement and related costs since these expenses are excluded from Adjusted EBITDAX. For the three months ended September 30, 2010, $25 million has been reclassified from the oil and gas exploration and production segment to the midstream segment to properly reflect the previously reported amounts.

[2] Operating costs and expenses exclude exploration expense; depreciation, depletion, and amortization; impairments; and Deepwater Horizon settlement and related costs since these expenses are excluded from Adjusted EBITDAX. For the nine months ended September 30, 2010, $57 million has been reclassified from the oil and gas exploration and production segment to the midstream segment to properly reflect the previously reported amounts.

[3] Represents the effect of marketing and trading derivative activities.

[4] In the fourth quarter of 2010, the Company revised the definition of Adjusted EBITDAX to exclude the impact of unrealized (gains) losses on derivative instruments, net. The prior periods have been adjusted to reflect this change.