Anadarko Petroleum 10-Q 4 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 31, 2013
Document And Entity Information [Abstract]	'	'
Entity Registrant Name	'ANADARKO PETROLEUM CORP	'
Entity Central Index Key	'0000773910	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-13	'
Amendment Flag	'false	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	503,266,938

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	3 Months Ended		9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues and Other	'	'	'	'
Natural-gas sales	$805	$613	$2,547	$1,682
Oil and condensate sales	2,389	2,163	6,761	6,629
Natural-gas liquids sales	325	289	889	913
Gathering, processing, and marketing sales	270	218	750	671
Gains (losses) on divestitures and other, net	64	49	296	106
Total	3,853	3,332	11,243	10,001
Costs and Expenses	'	'	'	'
Oil and gas operating	277	241	769	732
Oil and gas transportation and other	255	247	763	710
Exploration	272	297	714	1,662
Gathering, processing, and marketing	217	185	638	552
General and administrative	255	285	787	816
Depreciation, depletion, and amortization	996	979	2,958	2,936
Other taxes	294	267	819	970
Impairments	593	4	632	166
Algeria exceptional profits tax settlement	0	7	33	-1,797
Deepwater Horizon settlement and related costs	5	4	12	15
Total	3,164	2,516	8,125	6,762
Operating Income (Loss)	689	816	3,118	3,239
Other (Income) Expense	'	'	'	'
Interest expense	177	185	513	561
(Gains) losses on derivatives, net	72	251	-393	-77
Other (income) expense, net	-23	-10	69	-264
Total	226	426	189	220
Income (Loss) Before Income Taxes	463	390	2,929	3,019
Income tax expense (benefit)	240	248	1,263	764
Net Income (Loss)	223	142	1,666	2,255
Net income attributable to noncontrolling interests	41	21	95	67
Net Income (Loss) Attributable to Common Stockholders	$182	$121	$1,571	$2,188
Per Common Share	'	'	'	'
Net income (loss) attributable to common stockholders—basic	$0.36	$0.24	$3.11	$4.35
Net income (loss) attributable to common stockholders—diluted	$0.36	$0.24	$3.10	$4.34
Average Number of Common Shares Outstanding—Basic	503	500	502	499
Average Number of Common Shares Outstanding—Diluted	505	502	504	501
Dividends (per Common Share)	$0.18	$0.09	$0.36	$0.27

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Statement of Comprehensive Income [Abstract]	'		'		'		'
Net Income (Loss)	$223		$142		$1,666		$2,255
Other Comprehensive Income (Loss), net of taxes	'		'		'		'
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net (1)	2	[1]	2	[1]	5	[1]	6	[1]
Adjustments for pension and other postretirement plans	'		'		'		'
Amortization of net actuarial (gain) loss to general and administrative expense (2)	18	[2]	15	[2]	56	[2]	44	[2]
Amortization of net prior service (credit) cost to general and administrative expense	1		0		1		1
Total adjustments for pension and other postretirement plans	19		15		57		45
Total	21		17		62		51
Comprehensive Income (Loss)	244		159		1,728		2,306
Comprehensive income attributable to noncontrolling interests	41		21		95		67
Comprehensive Income (Loss) Attributable to Common Stockholders	$203		$138		$1,633		$2,239
[1]	Net of income tax benefit (expense) of $(1) million for the three months ended September 30, 2013, $(1) million for the three months ended September 30, 2012, $(3) million for the nine months ended September 30, 2013, and $(3) million for the nine months ended September 30, 2012.
[2]	Net of income tax benefit (expense) of $(11) million for the three months ended September 30, 2013, $(8) million for the three months ended September 30, 2012, $(32) million for the nine months ended September 30, 2013, and $(25) million for the nine months ended September 30, 2012.

CONSOLIDATED_STATEMENTS_OF_COM1

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]	'	'	'	'
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net, tax effect	($1)	($1)	($3)	($3)
Amortization of net actuarial (gain) loss to general and administrative expense, tax effect	($11)	($8)	($32)	($25)

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Current Assets	'	'
Cash and cash equivalents	$3,939	$2,471
Accounts receivable (net of allowance of $6 million and $7 million)	'	'
Customers	1,266	1,473
Others	1,199	1,274
Algeria exceptional profits tax settlement	0	730
Other current assets	736	847
Total	7,140	6,795
Properties and Equipment	'	'
Cost	69,167	63,598
Less accumulated depreciation, depletion, and amortization	28,682	25,200
Net properties and equipment	40,485	38,398
Other Assets	2,006	1,716
Goodwill and Other Intangible Assets	5,663	5,680
Total Assets	55,294	52,589
Current Liabilities	'	'
Accounts payable	3,070	2,989
Current asset retirement obligations	311	298
Accrued expenses	1,357	707
Total	4,738	3,994
Long-term Debt	13,647	13,269
Other Long-term Liabilities	'	'
Deferred income taxes	9,372	8,759
Asset retirement obligations	1,673	1,587
Other	1,963	3,098
Total	13,008	13,444
Stockholders' equity	'	'
Common stock, par value $0.10 per share (1.0 billion shares authorized, 521.7 million and 518.6 million shares issued)	52	51
Paid-in capital	8,521	8,230
Retained earnings	15,218	13,829
Treasury stock (18.5 million and 18.1 million shares)	-871	-841
Accumulated other comprehensive income (loss)	-578	-640
Total Stockholders’ Equity	22,342	20,629
Noncontrolling interests	1,559	1,253
Total Equity	23,901	21,882
Total Liabilities and Equity	$55,294	$52,589

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Allowance for uncollectible accounts	$6	$7
Common stock, par value	$0.10	$0.10
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	521,700,000	518,600,000
Treasury stock, shares	18,500,000	18,100,000

CONSOLIDATED_STATEMENTS_OF_EQU

CONSOLIDATED STATEMENTS OF EQUITY (USD $)	Total		Common Stock [Member]	Paid-in Capital [Member]		Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]
In Millions
Balance at Dec. 31, 2012	$21,882		$51	$8,230		$13,829	($841)	($640)	$1,253
Net income (loss)	1,666		'	'		1,571	'	'	95
Common stock issued	231		1	230		'	'	'	'
Dividends—common stock	-182		'	'		-182	'	'	'
Repurchase of common stock	-30		'	'		'	-30	'	'
Subsidiary equity transactions (1)	381		'	61	[1]	'	'	'	320
Distributions to noncontrolling interest owners	-111		'	'		'	'	'	-111
Contributions from noncontrolling interest owners	2		'	'		'	'	'	2
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	5	[2]	'	'		'	'	5	'
Adjustments for pension and other postretirement plans	57		'	'		'	'	57	'
Balance at Sep. 30, 2013	$23,901		$52	$8,521		$15,218	($871)	($578)	$1,559
[1]	The $61 million increase to paid-in capital, together with the Company’s net income (loss) attributable to common stockholders totaled $1,632 million for the nine months ended September 30, 2013.
[2]	Net of income tax benefit (expense) of $(1) million for the three months ended September 30, 2013, $(1) million for the three months ended September 30, 2012, $(3) million for the nine months ended September 30, 2013, and $(3) million for the nine months ended September 30, 2012.

CONSOLIDATED_STATEMENTS_OF_EQU1

CONSOLIDATED STATEMENTS OF EQUITY (Parenthetical) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Statement of Stockholders' Equity [Abstract]	'
Increase to paid-in capital for change in ownership interest upon equity issuance	$61
Net income (loss) attributable to common stockholders, including increase to paid-in capital for change in ownership interest upon equity issuance	$1,632

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash Flows from Operating Activities	'	'
Net income (loss)	$1,666	$2,255
Adjustments to reconcile net income (loss) to net cash provided by operating activities	'	'
Depreciation, depletion, and amortization	2,958	2,936
Deferred income taxes	535	95
Dry hole expense and impairments of unproved properties	423	1,389
Impairments	632	166
(Gains) losses on divestitures, net	-165	23
Unrealized (gains) losses on derivatives, net	-359	539
Other	174	174
Changes in assets and liabilities	'	'
Deepwater Horizon settlement and related costs	3	25
Algeria exceptional profits tax settlement	730	-1,183
Tronox-related contingent loss	0	-250
(Increase) decrease in accounts receivable	246	409
Increase (decrease) in accounts payable and accrued expenses	-37	-486
Other items—net	-22	27
Net cash provided by (used in) operating activities	6,784	6,119
Cash Flows from Investing Activities	'	'
Additions to properties and equipment and dry hole costs	-5,327	-5,448
Acquisition of businesses	-473	0
Divestitures of properties and equipment and other assets	451	440
Other—net	-552	-188
Net cash provided by (used in) investing activities	-5,901	-5,196
Cash Flows from Financing Activities	'	'
Borrowings, net of issuance costs	843	885
Repayments of debt	-495	-2,005
Increase (decrease) in outstanding checks	63	12
Dividends paid	-182	-136
Repurchase of common stock	-30	-26
Issuance of common stock, including tax benefit on share-based compensation awards	123	68
Sale of subsidiary units	418	212
Distributions to noncontrolling interest owners	-111	-81
Contributions from noncontrolling interest owners	2	14
Net cash provided by (used in) financing activities	631	-1,057
Effect of Exchange Rate Changes on Cash	-46	-31
Net Increase (Decrease) in Cash and Cash Equivalents	1,468	-165
Cash and Cash Equivalents at Beginning of Period	2,471	2,697
Cash and Cash Equivalents at End of Period	$3,939	$2,532

Summary_of_Significant_Account

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Summary of Significant Accounting Policies	'
	1. Summary of Significant Accounting Policies
	General    Anadarko Petroleum Corporation is engaged in the exploration, development, production, and marketing of natural gas, crude oil, condensate, and natural gas liquids (NGLs). In addition, the Company engages in the gathering, processing, treating, and transporting of natural gas, crude oil, and NGLs. Unless the context otherwise requires, the terms “Anadarko” and “Company” refer to Anadarko Petroleum Corporation and its consolidated subsidiaries.
	Basis of Presentation    The information furnished herein reflects all normal recurring adjustments that are, in the opinion of management, necessary for the fair presentation of the Company’s Consolidated Balance Sheets at September 30, 2013, and December 31, 2012, the Consolidated Statements of Income and Comprehensive Income for the three and nine months ended September 30, 2013 and 2012, the Consolidated Statements of Cash Flows for the nine months ended September 30, 2013 and 2012, and the Consolidated Statement of Equity for the nine months ended September 30, 2013. Certain prior-period amounts have been reclassified to conform to the current-period presentation.
	Use of Estimates    The preparation of financial statements in accordance with accounting principles generally accepted in the United States requires management to make informed judgments and estimates that affect the reported amounts of assets, liabilities, revenues, and expenses. Management evaluates its estimates and related assumptions regularly, including those related to the value of properties and equipment; proved reserves; goodwill; intangible assets; asset retirement obligations; litigation reserves; environmental liabilities; pension assets, liabilities, and costs; income taxes; and fair values. Changes in facts and circumstances or additional information may result in revised estimates, and actual results may differ from these estimates.

Inventories

Inventories	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Inventories	'
	2. Inventories
	The following summarizes the major classes of inventories included in other current assets:
		September 30,		December 31,
	millions	2013		2012
	Crude oil	$	102	$	91
	Natural gas	41		48
	NGLs	66		37
	Total	$	209	$	176

Acquisitions_and_Divestitures

Acquisitions and Divestitures	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Acquisitions and Divestitures	'
	3. Acquisitions and Divestitures
	Acquisitions    Anadarko and Western Gas Partners, LP (WES), a consolidated subsidiary of the Company, made several unrelated acquisitions during the nine months ended September 30, 2013. In March 2013, WES acquired a 33.75% interest in gas-gathering systems located in the Marcellus shale in north-central Pennsylvania for $135 million. In June 2013, WES acquired a 25% interest in a joint venture formed to design, construct, and own two fractionators located in Mont Belvieu, Texas for $78 million. In August 2013, Anadarko acquired certain oil and gas properties and related assets in the Moxa area of Wyoming for $310 million, including $306 million that represents the fair value of the oil and gas properties acquired. In September 2013, WES acquired an intrastate pipeline in southwestern Wyoming for $28 million.
	Divestitures    For the nine months ended September 30, 2013, proceeds from divestitures of $451 million and net gains on divestitures of $165 million were primarily related to the Company’s divestiture of its interests in a soda ash joint venture during the first quarter of 2013. In August 2013, the Company entered into a definitive agreement to sell a 10% working interest in Mozambique’s Offshore Area 1 for $2.64 billion. The transaction is subject to governmental approvals and other customary closing conditions, and is expected to close in late 2013 or early 2014.

Impairments

Impairments	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Impairments	'
	4. Impairments
	The following summarizes impairments by segment:
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	millions	2013		2012		2013		2012
	Oil and gas exploration and production
	Long-lived assets held for use
	U.S. onshore properties	$	—	$	2	$	—	$	81
	Gulf of Mexico properties	593		—		593		67
	Cost-method investment	—		1		10		12
	Midstream
	Long-lived assets held for use	—		1		29		6
	Impairments	$	593	$	4	$	632	$	166
	During the third quarter of 2013, certain Gulf of Mexico properties were impaired due to a reduction in estimated future net cash flows per barrel and downward revisions of reserves that the Company no longer plans to develop. The Company impaired its Venezuelan cost-method investment in 2013 and 2012 due to declines in estimated recoverable value. In addition, a midstream property was impaired during 2013 due to a reduction in estimated future cash flows. In 2012, certain U.S. onshore and midstream properties were impaired primarily due to lower natural-gas prices and a Gulf of Mexico property was impaired as a result of downward reserves revisions for a property that was near the end of its economic life.
	The following summarizes the post-impairment fair value of the above-described assets, by asset category and input level within the fair-value hierarchy:
	millions
	2013	Level 1		Level 2		Level 3 (1)		Total
	Long-lived assets held for use	$	—	$	—	$	266	$	266
	Cost-method investment (2)	—		—		32		32
	2012
	Long-lived assets held for use	$	—	$	—	$	38	$	38
	Cost-method investment (2)	—		—		34		34
	__________________________________________________________________
	(1)	The income approach was used to measure fair value.
	(2)	This represents the Company’s after-tax net investment.

Suspended_Exploratory_Well_Cos

Suspended Exploratory Well Costs	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Suspended Exploratory Well Costs	'
	5. Suspended Exploratory Well Costs
	The Company’s suspended exploratory well costs were $2.2 billion at September 30, 2013, and $2.1 billion at December 31, 2012. The increase in suspended exploratory well costs during 2013 is primarily related to the capitalization of costs associated with successful exploration drilling in the Gulf of Mexico, Brazil, and Mozambique. Management believes projects with suspended exploratory well costs exhibit sufficient quantities of hydrocarbons to justify potential development and is actively pursuing efforts to assess whether reserves can be attributed to these projects. If additional information becomes available that raises substantial doubt as to the economic or operational viability of any of these projects, the associated costs will be expensed at that time. During the nine months ended September 30, 2013, $95 million of exploratory well costs previously capitalized as suspended exploratory well costs for greater than one year at December 31, 2012, were charged to dry hole expense.

Noncontrolling_Interests

Noncontrolling Interests	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Noncontrolling Interests	'
	6. Noncontrolling Interests
	Western Gas Equity Partners, LP (WGP) is a consolidated subsidiary formed by Anadarko to own partnership interests in WES. At September 30, 2013, Anadarko’s ownership interest in WGP consisted of a 91.0% limited partner interest and the entire general partner interest.
	WES is a limited partnership formed by Anadarko to own, operate, acquire, and develop midstream assets. During 2013, WES has issued approximately seven million common units to the public, raising net proceeds of $419 million. At September 30, 2013, WGP’s ownership interest in WES consisted of a 43.1% limited partner interest, the entire 2.0% general partner interest, and all WES incentive distribution rights. At September 30, 2013, Anadarko also owned a 0.4% limited partner interest in WES through another subsidiary.

Derivative_Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Derivative Instruments	'
	7. Derivative Instruments
	Objective and Strategy    The Company uses derivative instruments to manage its exposure to cash-flow variability from commodity-price and interest-rate risks. Futures, swaps, and options are used to manage exposure to commodity-price risk inherent in the Company’s oil and natural-gas production and natural-gas processing operations (Oil and Natural-Gas Production/Processing Derivative Activities). Futures contracts and commodity-price swap agreements are used to fix the price of expected future oil and natural-gas sales at major industry trading locations, such as Henry Hub, Louisiana for natural gas and Cushing, Oklahoma or Sullom Voe, Scotland for oil. Basis swaps are periodically used to fix or float the price differential between product prices at one market location versus another. Options are used to establish a floor price, a ceiling price, or a floor and a ceiling price (collar) for expected future oil and natural-gas sales. Derivative instruments are also used to manage commodity-price risk inherent in customer price requirements and to fix margins on the future sale of natural gas and NGLs from the Company’s leased storage facilities (Marketing and Trading Derivative Activities).
	Interest-rate swaps are used to fix or float interest rates on existing or anticipated indebtedness. The purpose of these instruments is to manage the Company’s existing or anticipated exposure to unfavorable interest-rate changes. The fair value of the Company’s interest-rate swap portfolio increases (decreases) when interest rates increase (decrease).
	The Company does not apply hedge accounting to any of its derivative instruments. As a result, both realized and unrealized gains and losses associated with derivative instruments are recognized in earnings. Net derivative losses attributable to interest-rate derivatives previously subject to hedge accounting reside in accumulated other comprehensive income (loss) and are reclassified to earnings as the transactions to which the derivatives relate are recognized in earnings. See Note 10—Accumulated Other Comprehensive Income (Loss).
	7. Derivative Instruments (Continued)
	Oil and Natural-Gas Production/Processing Derivative Activities    The natural-gas prices listed below are New York Mercantile Exchange (NYMEX) Henry Hub prices. The crude-oil prices listed below are a combination of NYMEX West Texas Intermediate (WTI) and IntercontinentalExchange, Inc. (ICE) Brent prices. The following is a summary of the Company’s derivative instruments related to its Oil and Natural-Gas Production/Processing Derivative Activities at September 30, 2013:
		2013				2014
		Settlement				Settlement
	Natural Gas
	Two-Way Collars (thousand MMBtu/d)	600			(1)	—
	Average price per MMBtu
	Ceiling sold price (call)	$	4			$	—
	Floor purchased price (put)	$	3.18			$	—
	Three-Way Collars (thousand MMBtu/d)	—			(2)	600
	Average price per MMBtu
	Ceiling sold price (call)	$	—			$	5.01
	Floor purchased price (put)	$	—			$	3.75
	Floor sold price (put)	$	—			$	2.75
	Fixed-Price Contracts (thousand MMBtu/d)	1,185				600
	Average price per MMBtu	$	4			$	4.26
	Crude Oil
	Three-Way Collars (MBbls/d)	26				—
	Average price per barrel
	Ceiling sold price (call)	$	125.15			$	—
	Floor purchased price (put)	$	105			$	—
	Floor sold price (put)	$	85			$	—
	Fixed-Price Contracts (MBbls/d)	167				—
	Average price per barrel	$	102.74			$	—
	__________________________________________________________________
	(1)	The two-way collars have a contract term of April 2013 to October 2013.
	(2)	The Company entered into offsetting purchased and sold natural-gas three-way collars of 450,000 MMBtu/d for 2013 settlement.
	MMBtu—million British thermal units
	MMBtu/d—million British thermal units per day
	MBbls/d—thousand barrels per day
	A two-way collar is a combination of two options: a sold call and a purchased put. The sold call establishes the maximum price that the Company will receive for the contracted commodity volumes. The purchased put establishes the minimum price that the Company will receive for the contracted volumes.
	A three-way collar is a combination of three options: a sold call, a purchased put, and a sold put. The sold call establishes the maximum price that the Company will receive for the contracted commodity volumes. The purchased put establishes the minimum price that the Company will receive for the contracted volumes unless the market price for the commodity falls below the sold put strike price, at which point the minimum price equals the reference price (e.g., NYMEX) plus the excess of the purchased put strike price over the sold put strike price.
	7. Derivative Instruments (Continued)
	Marketing and Trading Derivative Activities    In addition to the positions in the previous table, the Company also engages in marketing and trading activities. These activities include physical product sales and related fixed-to-floating derivative transactions used to manage commodity-price risk. At September 30, 2013, and December 31, 2012, the Company had fixed-price physical transactions related to natural gas totaling 10 billion cubic feet (Bcf), offset by fixed-to-floating derivative transactions totaling 10 Bcf.
	Interest-Rate Derivatives    Anadarko has outstanding interest-rate swap contracts as a fixed-rate payer to mitigate the interest-rate risk associated with anticipated debt issuances. The Company locked in a fixed interest rate in exchange for a floating interest rate indexed to the three-month London Interbank Offered Rate. The swap instruments include a provision that requires both the termination of the swaps and cash settlement in full at the start of the reference period.
	The Company had the following outstanding interest-rate swaps at September 30, 2013:
	millions except percentages					Reference Period				Weighted-Average
	Notional Principal Amount					Start		End		Interest Rate
	$	750				Jun-14		Jun-24		6.00%
	$	1,100				Jun-14		Jun-44		5.57%
	$	50				Sep-16		Sep-26		5.91%
	$	750				Sep-16		Sep-46		5.86%
	Effect of Derivative Instruments—Balance Sheet    The following summarizes the fair value of the Company’s derivative instruments:
			Gross								Gross
			Derivative Assets								Derivative Liabilities
	millions		September 30,				December 31,				September 30,				December 31,
	Balance Sheet Classification		2013				2012				2013				2012
	Commodity derivatives
	Other current assets		$	359			$	475			$	(170	)		$	(197	)
	Other assets		50				24				(13		)		(7		)
	Accrued expenses		48				6				(61		)		(14		)
	Other liabilities		—				1				(2		)		(7		)
			457				506				(246		)		(225		)
	Interest-rate and other derivatives
	Accrued expenses (1)		—				—				(550		)		—
	Other liabilities (1)		—				—				(215		)		(1,194		)
			—				—				(765		)		(1,194		)
	Total derivatives		$	457			$	506			$	(1,011	)		$	(1,419	)
	__________________________________________________________________
-1	Interest-rate swaps with June 2014 maturity dates were reclassified from other liabilities to accrued expenses during the second quarter of 2013.
7. Derivative Instruments (Continued)
Effect of Derivative Instruments—Statement of Income    The following summarizes realized and unrealized gains and losses related to derivative instruments:
millions		Three Months Ended												Nine Months Ended
		September 30, 2013												September 30, 2013
Classification of (Gain) Loss Recognized		Realized				Unrealized				Total				Realized				Unrealized				Total
Commodity derivatives
Gathering, processing, and marketing sales (1)		$	2			$	(10	)		$	(8	)		$	9			$	(12	)		$	(3	)
(Gains) losses on derivatives, net		26				120				146				(46		)		81				35
Interest-rate and other derivatives
(Gains) losses on derivatives, net		—				(74		)		(74		)		—				(428		)		(428		)
Total (gains) losses on derivatives, net		$	28			$	36			$	64			$	(37	)		$	(359	)		$	(396	)
		Three Months Ended												Nine Months Ended
		September 30, 2012												September 30, 2012
Classification of (Gain) Loss Recognized		Realized				Unrealized				Total				Realized				Unrealized				Total
Commodity derivatives
Gathering, processing, and marketing sales (1)		$	3			$	5			$	8			$	—			$	18			$	18
(Gains) losses on derivatives, net		(200		)		437				237				(600		)		369				(231		)
Interest-rate and other derivatives
(Gains) losses on derivatives, net		—				14				14				2				152				154
Total (gains) losses on derivatives, net		$	(197	)		$	456			$	259			$	(598	)		$	539			$	(59	)
__________________________________________________________________
(1)	Represents the effect of marketing and trading derivative activities.
Credit-Risk Considerations    The financial integrity of exchange-traded contracts, which are subject to nominal credit risk, is assured by NYMEX or ICE through systems of financial safeguards and transaction guarantees. Over-the-counter traded swaps, options, and futures contracts expose the Company to counterparty credit risk. The Company monitors the creditworthiness of its counterparties, establishes credit limits according to the Company’s credit policies and guidelines, and assesses the impact on fair value of its counterparties’ creditworthiness. The Company has the ability to require cash collateral or letters of credit to mitigate its credit-risk exposure. The Company has netting agreements with financial institutions that permit net settlement of gross commodity derivative assets against gross commodity derivative liabilities, and routinely exercises its contractual right to offset realized gains against realized losses when settling with derivative counterparties.
In addition, the Company has setoff agreements with certain financial institutions that may be exercised in the event of default and provide for contract termination and net settlement across derivative types. At September 30, 2013, $305 million of the Company’s $1.0 billion gross derivative liability balance, and at December 31, 2012, $339 million of the Company’s $1.4 billion gross derivative liability balance, would have been eligible for setoff against the Company’s gross derivative asset balance in the event of default. Other than in the event of default, the Company does not net settle across derivative types.
Some of the Company’s derivative instruments are subject to provisions that can require full or partial collateralization or immediate settlement of the Company’s obligations if certain credit-risk-related provisions are triggered. However, most of the Company’s derivative counterparties maintain secured positions with respect to the Company’s derivative liabilities under the Company’s $5.0 billion senior secured revolving credit facility ($5.0 billion Facility), the available capacity of which is sufficient to secure potential obligations to such counterparties.
7. Derivative Instruments (Continued)
Unsecured derivative obligations may require immediate settlement or full collateralization if certain credit-risk-related provisions are triggered, such as the Company’s credit rating from major credit rating agencies declining to a level below investment grade. The aggregate fair value of derivative instruments with credit-risk-related contingent features for which a net liability position existed was $52 million (net of collateral) at September 30, 2013, and $94 million (net of collateral) at December 31, 2012. The current portion of these amounts was included in accrued expenses and the long-term portion of these amounts was included in other long-term liabilities—other on the Company’s Consolidated Balance Sheets.
Fair Value    Fair value of futures contracts is based on quoted prices in active markets for identical assets or liabilities, which represent Level 1 inputs. Valuations of physical-delivery purchase and sale agreements, over-the-counter financial swaps, and commodity option collars are based on similar transactions observable in active markets and industry-standard models that primarily rely on market-observable inputs. Inputs used to estimate the fair value of swaps and options include market-price curves; contract terms and prices; credit-risk adjustments; and, for Black-Scholes option valuations, implied market volatility and discount factors. Inputs used to estimate fair value in industry-standard models are categorized as Level 2 inputs because substantially all assumptions and inputs are observable in active markets throughout the full term of the instruments.
The following summarizes the fair value of the Company’s derivative assets and liabilities, by input level within the fair-value hierarchy:
millions
September 30, 2013	Level 1				Level 2				Level 3				Netting (1)				Collateral				Total
Assets
Commodity derivatives
Financial institutions	$	4			$	379			$	—			$	(226	)		$	(1	)		$	156
Other counterparties	—				74				—				(6		)		—				68
Total derivative assets	$	4			$	453			$	—			$	(232	)		$	(1	)		$	224
Liabilities
Commodity derivatives
Financial institutions	$	(4	)		$	(232	)		$	—			$	226			$	1			$	(9	)
Other counterparties	—				(10		)		—				6				—				(4		)
Interest-rate and other derivatives	—				(765		)		—				—				—				(765		)
Total derivative liabilities	$	(4	)		$	(1,007	)		$	—			$	232			$	1			$	(778	)
December 31, 2012
Assets
Commodity derivatives
Financial institutions	$	6			$	453			$	—			$	(206	)		$	—			$	253
Other counterparties	—				47				—				(5		)		—				42
Total derivative assets	$	6			$	500			$	—			$	(211	)		$	—			$	295
Liabilities
Commodity derivatives
Financial institutions	$	(6	)		$	(202	)		$	—			$	206			$	1			$	(1	)
Other counterparties	—				(17		)		—				5				—				(12		)
Interest-rate and other derivatives	—				(1,194		)		—				—				—				(1,194		)
Total derivative liabilities	$	(6	)		$	(1,413	)		$	—			$	211			$	1			$	(1,207	)
__________________________________________________________________
(1)	Represents the impact of netting commodity derivative assets and liabilities with counterparties where the Company has the contractual right and intends to net settle.

Debt_and_Interest_Expense

Debt and Interest Expense	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Debt and Interest Expense	'
	8. Debt and Interest Expense
	Debt    The Company’s outstanding debt is senior unsecured, except for borrowings, if any, under the $5.0 billion Facility. The following summarizes the Company’s outstanding debt:
		September 30,			December 31,
	millions	2013			2012
	Total debt at face value	$	15,302		$	14,952
	Net unamortized discounts and premiums (1)	(1,655		)	(1,683		)
	Total long-term debt	$	13,647		$	13,269
	__________________________________________________________________
	(1)	Unamortized discounts and premiums are amortized over the term of the related debt.
	Anadarko’s $500 million aggregate principal amount of 7.625% Senior Notes due March 2014 and $275 million aggregate principal amount of 5.750% Senior Notes due June 2014 are classified as long-term debt on the Company’s Consolidated Balance Sheets, as the Company has the ability and intent to refinance these obligations using long-term debt. The Zero-Coupon Senior Notes due 2036 (Zero Coupons) can be put to the Company in October of each year, which would cause the Company to repay up to the then-accreted value of the outstanding Zero Coupons. None of the Zero Coupons (accreted value of $718 million) were put to the Company in October 2013.
	Fair Value    The Company uses a market approach to determine fair value of its fixed-rate debt using observable market data, which results in a Level 2 fair-value measurement. The carrying amount of floating-rate debt approximates fair value as the interest rates are variable and reflective of market rates. The estimated fair value of the Company’s total borrowings was $15.8 billion at September 30, 2013, and $16.2 billion at December 31, 2012.
	Debt Activity    The following summarizes the Company’s debt activity during the nine months ended September 30, 2013:
		Carrying
	millions	Value			Description
	Balance at December 31, 2012	$	13,269
	Borrowings	385			WES revolving credit facility
	Other, net	9			Amortization of debt discounts and premiums
	Balance at March 31, 2013	$	13,663
	Borrowings	110			WES revolving credit facility
	Repayments	(245		)	WES revolving credit facility
	Other, net	10			Amortization of debt discounts and premiums
	Balance at June 30, 2013	$	13,538
	Issuance	250			WES 2.600% Senior Notes due 2018
	Borrowings	100			WES revolving credit facility
	Repayments	(250		)	WES revolving credit facility
	Other, net	9			Amortization of debt discounts and premiums
	Balance at September 30, 2013	$	13,647
	WES Borrowings    During the third quarter of 2013, WES repaid $250 million of outstanding borrowings under its five-year, $800 million senior unsecured revolving credit facility maturing in March 2016 (RCF) with net proceeds from its public offering of $250 million aggregate principal amount of 2.600% Senior Notes due 2018. At September 30, 2013, WES was in compliance with all covenants contained in its RCF, had outstanding borrowings under its RCF of $100 million at an interest rate of 1.68%, and had available borrowing capacity of $687 million ($800 million maximum capacity, less $100 million of outstanding borrowings and $13 million of outstanding letters of credit).
	8. Debt and Interest Expense (Continued)
	Interest Expense    The following summarizes interest expense:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
	millions	2013			2012			2013			2012
	Current debt, long-term debt, and other	$	240		$	238		$	710		$	724
	Capitalized interest	(63		)	(53		)	(197		)	(163		)
	Interest expense	$	177		$	185		$	513		$	561

Stockholders_Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Stockholders' Equity	'
	9. Stockholders’ Equity
	The reconciliation between basic and diluted earnings per share attributable to common stockholders is as follows:
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	millions except per-share amounts	2013		2012		2013		2012
	Net income (loss)
	Net income (loss) attributable to common stockholders	$	182	$	121	$	1,571	$	2,188
	Less distributions on participating securities	—		—		1		1
	Less undistributed income allocated to participating securities	1		1		9		13
	Basic	$	181	$	120	$	1,561	$	2,174
	Diluted	$	181	$	120	$	1,561	$	2,174
	Shares
	Average number of common shares outstanding—basic	503		500		502		499
	Dilutive effect of stock options	2		2		2		2
	Average number of common shares outstanding—diluted	505		502		504		501
	Excluded (1)	3		6		4		6
	Net income (loss) per common share
	Basic	$	0.36	$	0.24	$	3.11	$	4.35
	Diluted	$	0.36	$	0.24	$	3.1	$	4.34
	Dividends per common share	$	0.18	$	0.09	$	0.36	$	0.27
	__________________________________________________________________
	(1)	Inclusion of certain shares would have had an anti-dilutive effect.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Accumulated Other Comprehensive Income (Loss)	'
	10. Accumulated Other Comprehensive Income (Loss)
	The following summarizes the after-tax changes in the balances of each component of accumulated other comprehensive income (loss):
	millions	Interest-rate			Pension and Other Postretirement			Total
		Derivatives			Plans
		Previously
		Subject to Hedge
		Accounting
	Balance at December 31, 2012	$	(61	)	$	(579	)	$	(640	)
	Reclassifications to Consolidated Statement of Income	5			57			62
	Balance at September 30, 2013	$	(56	)	$	(522	)	$	(578	)

Commitments

Commitments	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Commitments	'
	11. Commitments
	In June 2013, the Company entered into a three-year operating lease agreement for a deepwater drillship expected to be delivered in late 2014. The lease obligation totals $464 million, with aggregate future annual minimum lease payments of $33 million in 2014, $154 million in 2015, $155 million in 2016, and $122 million in 2017.

Contingencies

Contingencies	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Contingencies	'
	12. Contingencies
	General    The Company is a defendant in a number of lawsuits and is involved in governmental proceedings and regulatory controls arising in the ordinary course of business, including, but not limited to, personal injury claims; title disputes; tax disputes; royalty claims; contract claims; contamination claims relating to oil and gas production, transportation, and processing; and environmental claims, including claims involving assets owned by acquired companies. Anadarko is also subject to various environmental-remediation and reclamation obligations arising from federal, state, and local laws and regulations. While the ultimate outcome and impact on the Company cannot be predicted with certainty, after consideration of recorded expense and liability accruals, management believes that the resolution of pending proceedings will not have a material adverse effect on the Company’s consolidated financial position, results of operations, or cash flows.
	The following is a discussion of the material developments with respect to the contingencies previously reported in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012, and material matters that have arisen since the filing of such report.
	Deepwater Horizon Events    In April 2010, the Macondo well in the Gulf of Mexico blew out and an explosion occurred on the Deepwater Horizon drilling rig. The well was operated by BP Exploration and Production Inc. (BP) and Anadarko held a 25% nonoperated interest. In October 2011, the Company and BP entered into a settlement agreement relating to the Deepwater Horizon events (Settlement Agreement). Pursuant to the Settlement Agreement, the Company is fully indemnified by BP against claims and damages arising under the Oil Pollution Act of 1990 (OPA), claims for natural resource damages (NRD) and assessment costs, and other potential damages. This indemnification is guaranteed by BP Corporation North America Inc. (BPCNA) and, in the event that the net worth of BPCNA declines below an agreed-upon amount, BP p.l.c. has agreed to become the sole guarantor. Under the Settlement Agreement, BP does not indemnify the Company against fines and penalties, punitive damages, shareholder derivative or securities laws claims, or certain other claims. The Company has not recorded a liability for any costs that are subject to indemnification by BP. For additional disclosure of the Deepwater Horizon events, the Company’s Settlement Agreement with BP, environmental claims under OPA, NRD claims, potential penalties and fines, and civil litigation, see Note 17—Contingencies—Deepwater Horizon Events in the Notes to the Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012.
	Penalties and Fines    In December 2010, the U.S. Department of Justice (DOJ), on behalf of the United States, filed a civil lawsuit in the U.S. District Court in New Orleans, Louisiana (Louisiana District Court) against several parties, including Anadarko, seeking an assessment of civil penalties under the Clean Water Act (CWA) in an amount to be determined by the Louisiana District Court. In February 2012, the Louisiana District Court entered a declaratory judgment that, as a partial owner of the Macondo well, Anadarko is liable for civil penalties under Section 311 of the CWA. The declaratory judgment addresses liability only, and does not address the amount of any civil penalty. The assessment of a civil penalty against Anadarko has been reserved until a later proceeding to be scheduled by the Louisiana District Court. In August 2012, Anadarko filed a notice of appeal in the U.S. Court of Appeals for the Fifth Circuit concerning that portion of the February 2012 declaratory judgment finding Anadarko liable for civil penalties under the CWA. The appeal is pending and oral arguments are set for December 2013.
	12. Contingencies (Continued)
	As discussed below, numerous Deepwater Horizon event-related civil lawsuits have been filed against BP and other parties, including the Company. Certain state and local governments have appealed, or have provided indication of a likely appeal of, the Louisiana District Court’s decision that only federal law, and not state law, applies to Deepwater Horizon event-related claims. If any such appeal is successful, state and/or local laws and regulations could become sources of penalties or fines against the Company.
	Applicable accounting guidance requires the Company to accrue a liability if it is probable that a liability is incurred and the amount of the liability can be reasonably estimated. The Louisiana District Court’s declaratory judgment in February 2012 satisfies the requirement that a loss, arising from the future assessment of a civil penalty against Anadarko, is probable. Notwithstanding the declaratory judgment, the Company currently cannot estimate the amount of any potential civil penalty. The CWA sets forth subjective criteria, including degree of fault and history of prior violations, which significantly influence the magnitude of CWA penalty assessments. As a result of the subjective nature of CWA penalty assessments, the Company currently cannot estimate the amount of any such penalty nor determine a range of potential loss. Furthermore, neither the February 2012 settlement of Deepwater Horizon-related civil penalties (including those under the CWA) by the other nonoperating partner with the United States and five affected Gulf states (Texas, Louisiana, Mississippi, Alabama, and Florida) nor the January 2013 settlement of CWA civil and criminal penalties by the drilling contractor with the United States affects the Company’s current conclusion regarding its ability to estimate potential fines and penalties. The Company lacks insight into those settlements, retains legal counsel separate from the other parties, and was not involved in any manner with respect to those settlements. Events or factors that could assist the Company in estimating the amount of any potential civil penalty or a range of potential loss related to such penalties include (i) an assessment by the DOJ, (ii) a ruling by a court of competent jurisdiction, or (iii) the initiation of substantive settlement negotiations between the Company and the DOJ.
	Given the Company’s lack of direct operational involvement in the event, as was reconfirmed by the Louisiana District Court in September 2013, and the subjective criteria of the CWA, the Company believes that its exposure to CWA penalties will not materially impact the Company’s consolidated financial position, results of operations, or cash flows.
	Civil Litigation Damage Claims    Numerous Deepwater Horizon event-related civil lawsuits have been filed against BP and other parties, including the Company. This litigation has been consolidated into a federal Multidistrict Litigation (MDL) action pending before Judge Carl Barbier in the Louisiana District Court. In March 2012, BP and the Plaintiffs’ Steering Committee entered into a tentative settlement agreement to resolve the substantial majority of economic loss and medical claims stemming from the Deepwater Horizon events, which the Louisiana District Court approved in orders issued in December 2012 and January 2013. Only OPA claims seeking economic loss damages against the Company remain. In addition, certain state and local governments have appealed, or have provided indication of a likely appeal of, the MDL court’s decision that only federal law, and not state law, applies to Deepwater Horizon event-related claims. The Company, pursuant to the Settlement Agreement, is fully indemnified by BP against losses arising as a result of claims for damages, irrespective of whether such claims are based on federal (including OPA) or state law.
	The first phase of the trial in the proceeding filed in the MDL by Transocean Ltd. (Transocean) under the Limitation of Liability Act commenced in February 2013 (Phase I). In April 2013, the evidence closed and all parties rested. Findings of fact, post-trial briefs, and responsive briefs were submitted in July 2013. BP, BP p.l.c., the United States, state and local governments, Halliburton Energy Services, Inc. (Halliburton), and Transocean participated in Phase I of the trial. Anadarko was excused from participation in Phase I of the trial. The issues tried in Phase I included the cause of the blow-out and all related events leading up to April 22, 2010, the date the Deepwater Horizon sank, as well as allocation of fault. The allocation of fault remains in the Phase I trial because Halliburton and Transocean have not settled with any of the parties and each wishes to prove to the court that their respective company was not at fault. The second phase of trial began in September 2013 (Phase II) and in October 2013 the evidence closed and all parties rested. The issues tried in Phase II included spill-source control and quantification of the spill for the period from April 22, 2010, until the well was capped. The Company, BP, BP p.l.c., the United States, state and local governments, Halliburton, and Transocean participated in Phase II of the trial. The judge entered an order prior to commencement of the Phase II trial excluding any evidence of Anadarko’s culpability or fault during Phase II of the trial.
	12. Contingencies (Continued)
	Two separate class action complaints were filed in June and August 2010, in the U.S. District Court for the Southern District of New York (New York District Court) on behalf of purported purchasers of the Company’s stock between June 9, 2009, and June 12, 2010, against Anadarko and certain of its officers. The complaints allege causes of action arising pursuant to the Securities Exchange Act of 1934 for purported misstatements and omissions regarding, among other things, the Company’s liability related to the Deepwater Horizon events. In November 2010, the New York District Court consolidated the two cases. In March 2012, the New York District Court granted the plaintiffs’ motion to transfer venue to the U.S. District Court for the Southern District of Texas - Houston Division (Texas District Court). In May 2012, the Texas District Court granted the defendants’ motion to transfer the consolidated action within the district to Judge Keith P. Ellison. In July 2012, the plaintiffs filed their First Amended Consolidated Class Action Complaint. The defendants filed a renewed motion to dismiss in the Texas District Court in September 2012. In July 2013, the Texas District Court dismissed the claims relating to all but one of the alleged misstatements asserted in the plaintiffs’ complaint. The Texas District Court gave the plaintiffs 30 days to amend the complaint to attempt to rehabilitate the claims that were dismissed. The plaintiffs declined to amend the complaint. The Company filed its answer to the complaint in September 2013.
	In September 2010, a purported shareholder made a demand on the Company’s Board of Directors (the Board) to investigate allegations of breaches of duty by members of management related to the Deepwater Horizon events. The Board received a supplemental demand letter from the shareholder in March 2012. The Board considered each of the demand letters in January 2011 and April 2012 and determined that it would not be in the best interest of the Company to pursue the issues alleged in the demand letters. In May 2013, a shareholder derivative petition was filed in the 215th District Court of Harris County, Texas by the shareholder against Anadarko (as a nominal defendant) and certain current and former directors and officers. The petition alleges breach of fiduciary duties, unjust enrichment, abuse of control, and gross mismanagement in connection with the Deepwater Horizon events. The plaintiff seeks an unspecified amount of damages, certain changes to the Company’s governance and internal procedures, disgorgement of profits, and reimbursement of litigation fees and costs.
	Given the various stages of these matters, the Company currently cannot assess the probability of losses, or reasonably estimate a range of any potential losses, related to ongoing proceedings. The Company intends to vigorously defend itself, its officers, and its directors in each of these matters, and will avail itself of the indemnities provided by BP against civil damages.
	Remaining Liability Outlook    It is reasonably possible that the Company may recognize additional Deepwater Horizon event-related liabilities for potential fines and penalties, shareholder claims, and certain other claims not covered by the indemnification provisions of the Settlement Agreement; however, the Company does not believe that any potential liability attributable to the foregoing items, individually or in the aggregate, will have a material impact on the Company’s consolidated financial position, results of operations, or cash flows. This assessment takes into account certain qualitative factors, including the subjective and fault-based nature of CWA penalties, the Company’s indemnification by BP against certain damage claims as discussed above, BP’s creditworthiness, the merits of the shareholder claims, and directors’ and officers’ insurance coverage related to outstanding shareholder claims.
	The Company will continue to monitor the MDL and other legal proceedings discussed above as well as federal investigations related to the Deepwater Horizon events. The Company cannot predict the nature of evidence that may be discovered during the course of legal proceedings or the timing of completion of any legal proceedings.
	Although the Company is fully indemnified by BP against OPA damage claims, NRD claims and assessment costs, and certain other potential liabilities, the Company may be required to recognize a liability for these amounts in advance of or in connection with recognizing a receivable from BP for the related indemnity payment. In all circumstances, however, the Company expects that any additional indemnified liability that may be recognized by the Company will be subsequently recovered from BP itself or through the guarantees of BPCNA or BP p.l.c.
	12. Contingencies (Continued)
	Tronox Litigation    In January 2009, Tronox Incorporated (Tronox), a former subsidiary of Kerr-McGee Corporation (Kerr-McGee), which is a current subsidiary of Anadarko, and certain of Tronox’s subsidiaries filed voluntary petitions for relief under Chapter 11 of the U.S. Bankruptcy Code in the U.S. Bankruptcy Court for the Southern District of New York (Bankruptcy Court). Subsequently, in May 2009, Tronox and certain of its affiliates filed a lawsuit against Anadarko and Kerr-McGee asserting a number of claims, including claims for actual and constructive fraudulent conveyance (Adversary Proceeding). Tronox alleges, among other things, that it was insolvent or undercapitalized at the time it was spun off from Kerr-McGee and seeks, among other things, to recover damages, including interest, in excess of $18.9 billion from Kerr-McGee and Anadarko, as well as litigation fees and costs. In accordance with Tronox’s Plan of Reorganization, the Adversary Proceeding is being pursued by the Anadarko Litigation Trust. Pursuant to the Anadarko Litigation Trust Agreement, the Anadarko Litigation Trust was “deemed substituted” for Tronox in the Adversary Proceeding as the party in such litigation. For purposes of this Form 10-Q, references to “Tronox” after February 2011 refer to the Anadarko Litigation Trust. For additional disclosure related to the Tronox Litigation, see Note 17—Contingencies—Tronox Litigation in the Notes to the Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012.
	The U.S. government was granted authority to intervene in the Adversary Proceeding, and in May 2009 asserted separate claims against Anadarko and Kerr-McGee under the Federal Debt Collection Procedures Act (FDCPA Complaint). Anadarko and Kerr-McGee moved to dismiss the claims of the U.S. government, but that motion has been stayed by the Bankruptcy Court. In April 2012, Anadarko and Kerr-McGee filed an answer to the FDCPA Complaint.
	In February 2012, the Company filed a motion for partial summary judgment seeking dismissal of several claims, including all actual and constructive fraudulent transfer claims protected by Section 546(e) of the Bankruptcy Code. The court has not yet ruled on that issue. Trial began in May 2012 and in September 2012, the evidence closed and both sides rested. In November 2012, the parties filed post-trial briefs and closing arguments were presented in December 2012. The parties filed final post-trial briefs in January 2013. The matter is pending before the court. To date, we have no information concerning the timing or form of decision that can be expected from the Bankruptcy Court in the Adversary Proceeding. Furthermore, Executive Benefits Insurance Agency v. Arkison, a case pending before the U.S. Supreme Court, raises certain legal issues including, but not limited to, whether affirmative consent is required for a bankruptcy court to have authority to enter a final judgment in a fraudulent transfer case. The Company is unable to determine the impact, if any, of this case on the substance or timing of a decision related to the Adversary Proceeding.
	The Company remains confident in the merits of its position and does not believe a loss resulting from litigating the Adversary Proceeding is probable. Accounting guidance requires that contingent losses be probable in nature for loss recognition to be appropriate. Accordingly, the Company’s Consolidated Balance Sheet at September 30, 2013, does not include a loss-contingency liability related to the litigation of the Adversary Proceeding.
	Although the Company does not consider a loss related to the litigation of the Adversary Proceeding to be probable, it is reasonably possible that the Company could incur a loss as a result of litigating this matter. Despite the plaintiffs’ damage claims in excess of $18.9 billion, the Company currently believes a reasonable range of potential loss is zero to $1.4 billion. The low end of the Company’s estimated range of potential loss is based on the Company’s current belief that it will more likely than not prevail in defending against the claims asserted in the Adversary Proceeding. The high end of the Company’s estimated range of potential loss represents the amount of consideration received by Kerr-McGee at the time of the Tronox spin-off, approximately $985 million, plus interest thereon.
	The Company’s estimated range of potential loss is based on the Company’s opinion regarding the current status of and likelihood of final resolution through litigation and could change as a result of developments in the Adversary Proceeding, or if the likelihood of settlement ceases to be remote. The Company’s ultimate financial obligation resulting from resolution of the Adversary Proceeding could vary, perhaps materially, from the Company’s above-stated estimated range of potential loss.
	12. Contingencies (Continued)
	Other    During the nine months ended September 30, 2013, the Company recognized a pretax loss of $131 million, reported in other (income) expense, net in the Consolidated Statement of Income, related to the cost to decommission wells and production facilities previously sold to a third party. In June 2013, as a result of a Chapter 11 bankruptcy declaration by the third party, the U.S. Department of the Interior ordered Anadarko to perform the decommissioning of the facility and related wells. These wells and production facilities are no longer owned by the Company nor are they related to its current operations. Anadarko expects to complete decommissioning of the production facilities in 2014 and the wells in 2015. Decommissioning obligations of $44 million were included in accrued expenses and $85 million were included in other long-term liabilities on the Consolidated Balance Sheet at September 30, 2013. Actual costs may vary from this estimate; however, the Company does not believe that such variation will materially impact its consolidated financial position, results of operations, or cash flows.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Income Taxes	'
	13. Income Taxes
	The following summarizes income tax expense (benefit) and effective tax rates:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
	millions except percentages	2013			2012			2013			2012
	Income tax expense (benefit)	$	240		$	248		$	1,263		$	764
	Effective tax rate	52		%	64		%	43		%	25		%
	The increase from the 35% U.S. federal statutory rate for the three and nine months ended September 30, 2013, and the three months ended September 30, 2012, was primarily attributable to the tax impact from foreign operations and Algerian exceptional profits taxes. The decrease from the 35% U.S. federal statutory rate for the nine months ended September 30, 2012, was primarily attributable to the non-taxable resolution of the Algeria exceptional profits tax dispute, partially offset by the tax impact from foreign operations and Algerian exceptional profits taxes.

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Supplemental Cash Flow Information	'
	14. Supplemental Cash Flow Information
	The following summarizes cash paid (received) for interest (net of amounts capitalized) and income taxes, as well as non-cash investing transactions:
		Nine Months Ended
		September 30,
	millions	2013		2012
	Cash paid (received)
	Interest	$	569	$	613
	Income taxes	$	137	$	(13	)
	Non-cash investing activities
	Fair value of properties and equipment received in non-cash exchange transactions	$	13	$	65

Segment_Information

Segment Information	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Segment Information	'
	15. Segment Information
	Anadarko’s business segments are separately managed due to distinct operational differences and unique technology, distribution, and marketing requirements. The Company’s three reporting segments are oil and gas exploration and production, midstream, and marketing. The oil and gas exploration and production segment explores for and produces natural gas, crude oil, condensate, and NGLs. The midstream segment engages in gathering, processing, treating, and transporting Anadarko and third-party oil, natural-gas, and NGLs production. The midstream reporting segment consists of two operating segments, WES and other midstream, which are aggregated into one reporting segment due to similar financial and operating characteristics. The marketing segment sells much of Anadarko’s production, as well as third-party purchased volumes.
	15. Segment Information (Continued)
	To assess the performance of Anadarko’s operating segments, the chief operating decision maker analyzes Adjusted EBITDAX. The Company defines Adjusted EBITDAX as income (loss) before income taxes; exploration expense; depreciation, depletion, and amortization (DD&A); impairments; interest expense; unrealized (gains) losses on derivatives, net; realized (gains) losses on interest-rate and other derivatives, net; and certain items not related to the Company’s normal operations, less net income attributable to noncontrolling interests. During the periods presented, these items included Deepwater Horizon settlement and related costs, Algeria exceptional profits tax settlement, Tronox-related contingent loss, and certain other nonoperating items included in other (income) expense, net. The Company’s definition of Adjusted EBITDAX excludes exploration expense, as it is not an indicator of operating efficiency for a given reporting period. However, exploration expense is monitored by management as part of costs incurred in exploration and development activities. Similarly, DD&A and impairments are excluded from Adjusted EBITDAX as a measure of segment operating performance because capital expenditures are evaluated at the time capital costs are incurred. Adjusted EBITDAX also excludes interest expense to allow for assessment of segment operating results without regard to Anadarko’s financing methods or capital structure. Finally, unrealized (gains) losses on derivatives, net and realized (gains) losses on interest-rate and other derivatives, net are excluded from Adjusted EBITDAX because these (gains) losses are not considered a measure of asset operating performance.
	Management believes that the presentation of Adjusted EBITDAX provides information useful in assessing the Company’s financial condition and results of operations and that Adjusted EBITDAX is a widely accepted financial indicator of a company’s ability to incur and service debt, fund capital expenditures, and make distributions to stockholders. Adjusted EBITDAX, as defined by Anadarko, may not be comparable to similarly titled measures used by other companies and should be considered in conjunction with net income (loss) attributable to common stockholders and other performance measures, such as operating income or cash flows from operating activities. Below is a reconciliation of consolidated Adjusted EBITDAX to income (loss) before income taxes:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
	millions	2013			2012			2013			2012
	Income (loss) before income taxes	$	463		$	390		$	2,929		$	3,019
	Exploration expense	272			297			714			1,662
	DD&A	996			979			2,958			2,936
	Impairments	593			4			632			166
	Interest expense	177			185			513			561
	Unrealized (gains) losses on derivatives, net	36			456			(359		)	539
	Realized (gains) losses on interest-rate and other derivatives, net	—			—			—			2
	Deepwater Horizon settlement and related costs	5			4			12			15
	Algeria exceptional profits tax settlement	—			7			33			(1,797		)
	Tronox-related contingent loss	—			—			—			(250		)
	Certain other nonoperating items	(10		)	—			75			—
	Less net income attributable to noncontrolling interests	41			21			95			67
	Consolidated Adjusted EBITDAX	$	2,491		$	2,301		$	7,412		$	6,786
	15. Segment Information (Continued)
	Information presented below as “Other and Intersegment Eliminations” includes results from hard-minerals royalty arrangements and corporate, financing, and certain hedging activities. The following summarizes selected financial information for Anadarko’s reporting segments:
	millions	Oil and Gas			Midstream			Marketing			Other and			Total
		Exploration									Intersegment
		& Production									Eliminations
	Three Months Ended September 30, 2013
	Sales revenues	$	1,916		$	95		$	1,778		$	—		$	3,789
	Intersegment revenues	1,516			287			(1,629		)	(174		)	—
	Gains (losses) on divestitures and other, net	7			—			—			57			64
	Total revenues and other	3,439			382			149			(117		)	3,853
	Operating costs and expenses (1)	930			216			164			(12		)	1,298
	Realized (gains) losses on commodity	—			—			—			26			26
	derivatives, net
	Other (income) expense, net (2)	—			—			—			(13		)	(13		)
	Net income attributable to noncontrolling interests	—			41			—			—			41
	Total expenses and other	930			257			164			1			1,352
	Unrealized (gains) losses on derivatives, net	—			—			(10		)	—			(10		)
	included in marketing revenue
	Adjusted EBITDAX	$	2,509		$	125		$	(25	)	$	(118	)	$	2,491
	Three Months Ended September 30, 2012
	Sales revenues	$	1,393		$	80		$	1,810		$	—		$	3,283
	Intersegment revenues	1,587			232			(1,682		)	(137		)	—
	Gains (losses) on divestitures and other, net	12			(6		)	—			43			49
	Total revenues and other	2,992			306			128			(94		)	3,332
	Operating costs and expenses (1)	840			182			152			51			1,225
	Realized (gains) losses on commodity	—			—			—			(200		)	(200		)
	derivatives, net
	Other (income) expense, net (2)	—			—			—			(10		)	(10		)
	Net income attributable to noncontrolling interests	—			21			—			—			21
	Total expenses and other	840			203			152			(159		)	1,036
	Unrealized (gains) losses on derivatives, net	—			—			5			—			5
	included in marketing revenue
	Adjusted EBITDAX	$	2,152		$	103		$	(19	)	$	65		$	2,301
	__________________________________________________________________
	(1)	Operating costs and expenses excludes exploration expense, DD&A, impairments, Deepwater Horizon settlement and related costs, and Algeria exceptional profits tax settlement since these expenses are excluded from Adjusted EBITDAX.
	(2)	Other (income) expense, net excludes Tronox-related contingent loss and certain other nonoperating items since these expenses are excluded from Adjusted EBITDAX.
	15. Segment Information (Continued)
	millions	Oil and Gas			Midstream			Marketing			Other and			Total
		Exploration									Intersegment
		& Production									Eliminations
	Nine Months Ended September 30, 2013
	Sales revenues	$	5,044		$	267		$	5,636		$	—		$	10,947
Intersegment revenues	4,904			805			(5,234		)	(475		)	—
Gains (losses) on divestitures and other, net	12			—			—			284			296
Total revenues and other	9,960			1,072			402			(191		)	11,243
Operating costs and expenses (1)	2,656			613			492			15			3,776
Realized (gains) losses on commodity	—			—			—			(46		)	(46		)
derivatives, net
Other (income) expense, net (2)	—			—			—			(6		)	(6		)
Net income attributable to noncontrolling interests	—			95			—			—			95
Total expenses and other	2,656			708			492			(37		)	3,819
Unrealized (gains) losses on derivatives, net	—			—			(12		)	—			(12		)
included in marketing revenue
Adjusted EBITDAX	$	7,304		$	364		$	(102	)	$	(154	)	$	7,412
Nine Months Ended September 30, 2012
Sales revenues	$	5,180		$	248		$	4,467		$	—		$	9,895
Intersegment revenues	3,796			701			(4,101		)	(396		)	—
Gains (losses) on divestitures and other, net	(17		)	(8		)	—			131			106
Total revenues and other	8,959			941			366			(265		)	10,001
Operating costs and expenses (1)	2,639			545			464			132			3,780
Realized (gains) losses on commodity	—			—			—			(600		)	(600		)
derivatives, net
Other (income) expense, net (2)	—			—			—			(14		)	(14		)
Net income attributable to noncontrolling interests	—			67			—			—			67
Total expenses and other	2,639			612			464			(482		)	3,233
Unrealized (gains) losses on derivatives, net	—			—			18			—			18
included in marketing revenue
Adjusted EBITDAX	$	6,320		$	329		$	(80	)	$	217		$	6,786
__________________________________________________________________
(1)	Operating costs and expenses excludes exploration expense, DD&A, impairments, Deepwater Horizon settlement and related costs, and Algeria exceptional profits tax settlement since these expenses are excluded from Adjusted EBITDAX.
(2)	Other (income) expense, net excludes Tronox-related contingent loss and certain other nonoperating items since these expenses are excluded from Adjusted EBITDAX.

Pension_Plans_and_Other_Postre

Pension Plans and Other Postretirement Benefits	9 Months Ended
	Sep. 30, 2013
Disclosure Text Block [Abstract]	'
Pension Plans and Other Postretirement Benefits	'
	16. Pension Plans and Other Postretirement Benefits
	The Company has contributory and non-contributory defined-benefit pension plans, which include both qualified and supplemental plans. The Company also provides certain health care and life insurance benefits for certain retired employees. Retiree health care benefits are funded by contributions from the retiree, and in certain circumstances, contributions from the Company. The Company’s retiree life insurance plan is noncontributory.
	During the nine months ended September 30, 2013, the Company made contributions of $122 million to its funded pension plans, $6 million to its unfunded pension plans, and $11 million to its unfunded other postretirement benefit plans. During the fourth quarter of 2013, the Company expects to contribute $2 million to its funded pension plans, $30 million to its unfunded pension plans, and $5 million to its unfunded other postretirement benefit plans.
	The following summarizes the Company’s pension and other postretirement benefit cost:
		Pension Benefits						Other Benefits
	millions	2013			2012			2013		2012
	Three Months Ended September 30
	Service cost	$	21		$	19		$	2	$	2
	Interest cost	19			21			3		4
	Expected return on plan assets	(22		)	(23		)	—		—
	Amortization of net actuarial loss (gain)	29			23			—		—
	Amortization of net prior service cost (credit)	—			—			1		—
	Net periodic benefit cost	$	47		$	40		$	6	$	6
	Nine Months Ended September 30
	Service cost	$	64		$	57		$	7	$	7
	Interest cost	58			64			10		12
	Expected return on plan assets	(68		)	(68		)	—		—
	Amortization of net actuarial loss (gain)	88			69			—		—
	Amortization of net prior service cost (credit)	—			—			1		1
	Net periodic benefit cost	$	142		$	122		$	18	$	20

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2013
Policy Text Block [Abstract]	'
Use of Estimates	'
	Use of Estimates    The preparation of financial statements in accordance with accounting principles generally accepted in the United States requires management to make informed judgments and estimates that affect the reported amounts of assets, liabilities, revenues, and expenses. Management evaluates its estimates and related assumptions regularly, including those related to the value of properties and equipment; proved reserves; goodwill; intangible assets; asset retirement obligations; litigation reserves; environmental liabilities; pension assets, liabilities, and costs; income taxes; and fair values. Changes in facts and circumstances or additional information may result in revised estimates, and actual results may differ from these estimates.

Inventories_Tables

Inventories (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Inventory Disclosure Table	'
	The following summarizes the major classes of inventories included in other current assets:
		September 30,		December 31,
	millions	2013		2012
	Crude oil	$	102	$	91
	Natural gas	41		48
	NGLs	66		37
	Total	$	209	$	176

Impairments_Tables

Impairments (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Schedule of Impairment Expense	'
	The following summarizes impairments by segment:
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	millions	2013		2012		2013		2012
	Oil and gas exploration and production
	Long-lived assets held for use
	U.S. onshore properties	$	—	$	2	$	—	$	81
	Gulf of Mexico properties	593		—		593		67
	Cost-method investment	—		1		10		12
	Midstream
	Long-lived assets held for use	—		1		29		6
	Impairments	$	593	$	4	$	632	$	166
Nonrecurring Fair Value Measurements Table	'
	The following summarizes the post-impairment fair value of the above-described assets, by asset category and input level within the fair-value hierarchy:
	millions
	2013	Level 1		Level 2		Level 3 (1)		Total
	Long-lived assets held for use	$	—	$	—	$	266	$	266
	Cost-method investment (2)	—		—		32		32
	2012
	Long-lived assets held for use	$	—	$	—	$	38	$	38
	Cost-method investment (2)	—		—		34		34
	__________________________________________________________________
	(1)	The income approach was used to measure fair value.
	(2)	This represents the Company’s after-tax net investment.

Derivative_Instruments_Tables

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Schedule of Derivative Instruments	'
	The following is a summary of the Company’s derivative instruments related to its Oil and Natural-Gas Production/Processing Derivative Activities at September 30, 2013:
		2013				2014
		Settlement				Settlement
	Natural Gas
	Two-Way Collars (thousand MMBtu/d)	600			(1)	—
	Average price per MMBtu
	Ceiling sold price (call)	$	4			$	—
	Floor purchased price (put)	$	3.18			$	—
	Three-Way Collars (thousand MMBtu/d)	—			(2)	600
	Average price per MMBtu
	Ceiling sold price (call)	$	—			$	5.01
	Floor purchased price (put)	$	—			$	3.75
	Floor sold price (put)	$	—			$	2.75
	Fixed-Price Contracts (thousand MMBtu/d)	1,185				600
	Average price per MMBtu	$	4			$	4.26
	Crude Oil
	Three-Way Collars (MBbls/d)	26				—
	Average price per barrel
	Ceiling sold price (call)	$	125.15			$	—
	Floor purchased price (put)	$	105			$	—
	Floor sold price (put)	$	85			$	—
	Fixed-Price Contracts (MBbls/d)	167				—
	Average price per barrel	$	102.74			$	—
	__________________________________________________________________
	-1	The two-way collars have a contract term of April 2013 to October 2013.
	-2	The Company entered into offsetting purchased and sold natural-gas three-way collars of 450,000 MMBtu/d for 2013 settlement.
	MMBtu—million British thermal units
	MMBtu/d—million British thermal units per day
	MBbls/d—thousand barrels per day
	The Company had the following outstanding interest-rate swaps at September 30, 2013:
	millions except percentages					Reference Period				Weighted-Average
	Notional Principal Amount					Start		End		Interest Rate
	$	750				Jun-14		Jun-24		6.00%
	$	1,100				Jun-14		Jun-44		5.57%
	$	50				Sep-16		Sep-26		5.91%
	$	750				Sep-16		Sep-46		5.86%
Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location	'
	The following summarizes the fair value of the Company’s derivative instruments:
			Gross								Gross
			Derivative Assets								Derivative Liabilities
	millions		September 30,				December 31,				September 30,				December 31,
	Balance Sheet Classification		2013				2012				2013				2012
	Commodity derivatives
	Other current assets		$	359			$	475			$	(170	)		$	(197	)
	Other assets		50				24				(13		)		(7		)
	Accrued expenses		48				6				(61		)		(14		)
	Other liabilities		—				1				(2		)		(7		)
			457				506				(246		)		(225		)
	Interest-rate and other derivatives
	Accrued expenses (1)		—				—				(550		)		—
	Other liabilities (1)		—				—				(215		)		(1,194		)
			—				—				(765		)		(1,194		)
	Total derivatives		$	457			$	506			$	(1,011	)		$	(1,419	)
	__________________________________________________________________
	-1	Interest-rate swaps with June 2014 maturity dates were reclassified from other liabilities to accrued expenses during the second quarter of 2013.
	The following summarizes realized and unrealized gains and losses related to derivative instruments:
	millions		Three Months Ended												Nine Months Ended
			September 30, 2013												September 30, 2013
	Classification of (Gain) Loss Recognized		Realized				Unrealized				Total				Realized				Unrealized				Total
	Commodity derivatives
	Gathering, processing, and marketing sales (1)		$	2			$	(10	)		$	(8	)		$	9			$	(12	)		$	(3	)
	(Gains) losses on derivatives, net		26				120				146				(46		)		81				35
	Interest-rate and other derivatives
	(Gains) losses on derivatives, net		—				(74		)		(74		)		—				(428		)		(428		)
	Total (gains) losses on derivatives, net		$	28			$	36			$	64			$	(37	)		$	(359	)		$	(396	)
			Three Months Ended												Nine Months Ended
			September 30, 2012												September 30, 2012
	Classification of (Gain) Loss Recognized		Realized				Unrealized				Total				Realized				Unrealized				Total
	Commodity derivatives
	Gathering, processing, and marketing sales (1)		$	3			$	5			$	8			$	—			$	18			$	18
	(Gains) losses on derivatives, net		(200		)		437				237				(600		)		369				(231		)
	Interest-rate and other derivatives
	(Gains) losses on derivatives, net		—				14				14				2				152				154
	Total (gains) losses on derivatives, net		$	(197	)		$	456			$	259			$	(598	)		$	539			$	(59	)
	__________________________________________________________________
	-1	Represents the effect of marketing and trading derivative activities.
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	'
	The following summarizes the fair value of the Company’s derivative assets and liabilities, by input level within the fair-value hierarchy:
	millions
	September 30, 2013	Level 1				Level 2				Level 3				Netting (1)				Collateral				Total
	Assets
	Commodity derivatives
	Financial institutions	$	4			$	379			$	—			$	(226	)		$	(1	)		$	156
	Other counterparties	—				74				—				(6		)		—				68
	Total derivative assets	$	4			$	453			$	—			$	(232	)		$	(1	)		$	224
	Liabilities
	Commodity derivatives
	Financial institutions	$	(4	)		$	(232	)		$	—			$	226			$	1			$	(9	)
	Other counterparties	—				(10		)		—				6				—				(4		)
	Interest-rate and other derivatives	—				(765		)		—				—				—				(765		)
	Total derivative liabilities	$	(4	)		$	(1,007	)		$	—			$	232			$	1			$	(778	)
	December 31, 2012
	Assets
	Commodity derivatives
	Financial institutions	$	6			$	453			$	—			$	(206	)		$	—			$	253
	Other counterparties	—				47				—				(5		)		—				42
	Total derivative assets	$	6			$	500			$	—			$	(211	)		$	—			$	295
	Liabilities
	Commodity derivatives
	Financial institutions	$	(6	)		$	(202	)		$	—			$	206			$	1			$	(1	)
	Other counterparties	—				(17		)		—				5				—				(12		)
	Interest-rate and other derivatives	—				(1,194		)		—				—				—				(1,194		)
	Total derivative liabilities	$	(6	)		$	(1,413	)		$	—			$	211			$	1			$	(1,207	)
	__________________________________________________________________
	(1)	Represents the impact of netting commodity derivative assets and liabilities with counterparties where the Company has the contractual right and intends to net settle.

Debt_and_Interest_Expense_Tabl

Debt and Interest Expense (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Debt Outstanding and Debt Activity Tables	'
	The following summarizes the Company’s outstanding debt:
		September 30,			December 31,
	millions	2013			2012
	Total debt at face value	$	15,302		$	14,952
	Net unamortized discounts and premiums (1)	(1,655		)	(1,683		)
	Total long-term debt	$	13,647		$	13,269
	__________________________________________________________________
	-1	Unamortized discounts and premiums are amortized over the term of the related debt.
	The following summarizes the Company’s debt activity during the nine months ended September 30, 2013:
		Carrying
	millions	Value			Description
	Balance at December 31, 2012	$	13,269
	Borrowings	385			WES revolving credit facility
	Other, net	9			Amortization of debt discounts and premiums
	Balance at March 31, 2013	$	13,663
	Borrowings	110			WES revolving credit facility
	Repayments	(245		)	WES revolving credit facility
	Other, net	10			Amortization of debt discounts and premiums
	Balance at June 30, 2013	$	13,538
	Issuance	250			WES 2.600% Senior Notes due 2018
	Borrowings	100			WES revolving credit facility
	Repayments	(250		)	WES revolving credit facility
	Other, net	9			Amortization of debt discounts and premiums
	Balance at September 30, 2013	$	13,647
Interest Expense Table	'
	The following summarizes interest expense:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
	millions	2013			2012			2013			2012
	Current debt, long-term debt, and other	$	240		$	238		$	710		$	724
	Capitalized interest	(63		)	(53		)	(197		)	(163		)
	Interest expense	$	177		$	185		$	513		$	561

Stockholders_Equity_Tables

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Earnings Per Share Table	'
	The reconciliation between basic and diluted earnings per share attributable to common stockholders is as follows:
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	millions except per-share amounts	2013		2012		2013		2012
	Net income (loss)
	Net income (loss) attributable to common stockholders	$	182	$	121	$	1,571	$	2,188
	Less distributions on participating securities	—		—		1		1
	Less undistributed income allocated to participating securities	1		1		9		13
	Basic	$	181	$	120	$	1,561	$	2,174
	Diluted	$	181	$	120	$	1,561	$	2,174
	Shares
	Average number of common shares outstanding—basic	503		500		502		499
	Dilutive effect of stock options	2		2		2		2
	Average number of common shares outstanding—diluted	505		502		504		501
	Excluded (1)	3		6		4		6
	Net income (loss) per common share
	Basic	$	0.36	$	0.24	$	3.11	$	4.35
	Diluted	$	0.36	$	0.24	$	3.1	$	4.34
	Dividends per common share	$	0.18	$	0.09	$	0.36	$	0.27
	__________________________________________________________________
	(1)	Inclusion of certain shares would have had an anti-dilutive effect.

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Schedule Of Accumulated Other Comprehensive Income (Loss) Table	'
	The following summarizes the after-tax changes in the balances of each component of accumulated other comprehensive income (loss):
	millions	Interest-rate			Pension and Other Postretirement			Total
		Derivatives			Plans
		Previously
		Subject to Hedge
		Accounting
	Balance at December 31, 2012	$	(61	)	$	(579	)	$	(640	)
	Reclassifications to Consolidated Statement of Income	5			57			62
	Balance at September 30, 2013	$	(56	)	$	(522	)	$	(578	)

Income_Taxes_Tables

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Schedule of Income Taxes and Effective Tax Rate	'
	The following summarizes income tax expense (benefit) and effective tax rates:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
	millions except percentages	2013			2012			2013			2012
	Income tax expense (benefit)	$	240		$	248		$	1,263		$	764
	Effective tax rate	52		%	64		%	43		%	25		%

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Supplemental Cash Flow Table	'
	The following summarizes cash paid (received) for interest (net of amounts capitalized) and income taxes, as well as non-cash investing transactions:
		Nine Months Ended
		September 30,
	millions	2013		2012
	Cash paid (received)
	Interest	$	569	$	613
	Income taxes	$	137	$	(13	)
	Non-cash investing activities
	Fair value of properties and equipment received in non-cash exchange transactions	$	13	$	65

Segment_Information_Tables

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Reconciliation of Consolidated Adjusted EBITDAX to Income (Loss) before Income Taxes	'
	Below is a reconciliation of consolidated Adjusted EBITDAX to income (loss) before income taxes:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
	millions	2013			2012			2013			2012
	Income (loss) before income taxes	$	463		$	390		$	2,929		$	3,019
	Exploration expense	272			297			714			1,662
	DD&A	996			979			2,958			2,936
	Impairments	593			4			632			166
	Interest expense	177			185			513			561
	Unrealized (gains) losses on derivatives, net	36			456			(359		)	539
	Realized (gains) losses on interest-rate and other derivatives, net	—			—			—			2
	Deepwater Horizon settlement and related costs	5			4			12			15
	Algeria exceptional profits tax settlement	—			7			33			(1,797		)
	Tronox-related contingent loss	—			—			—			(250		)
	Certain other nonoperating items	(10		)	—			75			—
	Less net income attributable to noncontrolling interests	41			21			95			67
	Consolidated Adjusted EBITDAX	$	2,491		$	2,301		$	7,412		$	6,786
Schedule of Segment Reporting Information, by Segment	'
	The following summarizes selected financial information for Anadarko’s reporting segments:
		Oil and Gas									Other and
		Exploration									Intersegment
	millions	& Production			Midstream			Marketing			Eliminations			Total
	Three Months Ended September 30, 2013
	Sales revenues	$	1,916		$	95		$	1,778		$	—		$	3,789
	Intersegment revenues	1,516			287			(1,629		)	(174		)	—
	Gains (losses) on divestitures and other, net	7			—			—			57			64
	Total revenues and other	3,439			382			149			(117		)	3,853
	Operating costs and expenses (1)	930			216			164			(12		)	1,298
	Realized (gains) losses on commodity	—			—			—			26			26
	derivatives, net
	Other (income) expense, net (2)	—			—			—			(13		)	(13		)
	Net income attributable to noncontrolling interests	—			41			—			—			41
	Total expenses and other	930			257			164			1			1,352
	Unrealized (gains) losses on derivatives, net	—			—			(10		)	—			(10		)
	included in marketing revenue
	Adjusted EBITDAX	$	2,509		$	125		$	(25	)	$	(118	)	$	2,491
	Three Months Ended September 30, 2012
	Sales revenues	$	1,393		$	80		$	1,810		$	—		$	3,283
	Intersegment revenues	1,587			232			(1,682		)	(137		)	—
	Gains (losses) on divestitures and other, net	12			(6		)	—			43			49
	Total revenues and other	2,992			306			128			(94		)	3,332
	Operating costs and expenses (1)	840			182			152			51			1,225
	Realized (gains) losses on commodity	—			—			—			(200		)	(200		)
	derivatives, net
	Other (income) expense, net (2)	—			—			—			(10		)	(10		)
	Net income attributable to noncontrolling interests	—			21			—			—			21
	Total expenses and other	840			203			152			(159		)	1,036
	Unrealized (gains) losses on derivatives, net	—			—			5			—			5
	included in marketing revenue
	Adjusted EBITDAX	$	2,152		$	103		$	(19	)	$	65		$	2,301
		Oil and Gas									Other and
		Exploration									Intersegment
	millions	& Production			Midstream			Marketing			Eliminations			Total
	Nine Months Ended September 30, 2013
	Sales revenues	$	5,044		$	267		$	5,636		$	—		$	10,947
	Intersegment revenues	4,904			805			(5,234		)	(475		)	—
	Gains (losses) on divestitures and other, net	12			—			—			284			296
	Total revenues and other	9,960			1,072			402			(191		)	11,243
	Operating costs and expenses (1)	2,656			613			492			15			3,776
	Realized (gains) losses on commodity	—			—			—			(46		)	(46		)
	derivatives, net
	Other (income) expense, net (2)	—			—			—			(6		)	(6		)
	Net income attributable to noncontrolling interests	—			95			—			—			95
	Total expenses and other	2,656			708			492			(37		)	3,819
	Unrealized (gains) losses on derivatives, net	—			—			(12		)	—			(12		)
	included in marketing revenue
	Adjusted EBITDAX	$	7,304		$	364		$	(102	)	$	(154	)	$	7,412
	Nine Months Ended September 30, 2012
	Sales revenues	$	5,180		$	248		$	4,467		$	—		$	9,895
	Intersegment revenues	3,796			701			(4,101		)	(396		)	—
	Gains (losses) on divestitures and other, net	(17		)	(8		)	—			131			106
	Total revenues and other	8,959			941			366			(265		)	10,001
	Operating costs and expenses (1)	2,639			545			464			132			3,780
	Realized (gains) losses on commodity	—			—			—			(600		)	(600		)
	derivatives, net
	Other (income) expense, net (2)	—			—			—			(14		)	(14		)
	Net income attributable to noncontrolling interests	—			67			—			—			67
	Total expenses and other	2,639			612			464			(482		)	3,233
	Unrealized (gains) losses on derivatives, net	—			—			18			—			18
	included in marketing revenue
	Adjusted EBITDAX	$	6,320		$	329		$	(80	)	$	217		$	6,786
__________________________________________________________________
(1)	Operating costs and expenses excludes exploration expense, DD&A, impairments, Deepwater Horizon settlement and related costs, and Algeria exceptional profits tax settlement since these expenses are excluded from Adjusted EBITDAX.
(2)	Other (income) expense, net excludes Tronox-related contingent loss and certain other nonoperating items since these expenses are excluded from Adjusted EBITDAX.

Pension_Plans_and_Other_Postre1

Pension Plans and Other Postretirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2013
Table Text Block [Abstract]	'
Components of Net Periodic Benefit Cost Table	'
	The following summarizes the Company’s pension and other postretirement benefit cost:
		Pension Benefits						Other Benefits
	millions	2013			2012			2013		2012
	Three Months Ended September 30
	Service cost	$	21		$	19		$	2	$	2
	Interest cost	19			21			3		4
	Expected return on plan assets	(22		)	(23		)	—		—
	Amortization of net actuarial loss (gain)	29			23			—		—
	Amortization of net prior service cost (credit)	—			—			1		—
	Net periodic benefit cost	$	47		$	40		$	6	$	6
	Nine Months Ended September 30
	Service cost	$	64		$	57		$	7	$	7
	Interest cost	58			64			10		12
	Expected return on plan assets	(68		)	(68		)	—		—
	Amortization of net actuarial loss (gain)	88			69			—		—
	Amortization of net prior service cost (credit)	—			—			1		1
	Net periodic benefit cost	$	142		$	122		$	18	$	20

Inventories_Detail

Inventories (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Energy Related Inventory [Abstract]	'	'
Crude oil	$102	$91
Natural gas	41	48
NGLs	66	37
Total	$209	$176

Acquisitions_and_Divestitures_

Acquisitions and Divestitures - Acquisitions (Detail) (USD $)	9 Months Ended		1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2013	Aug. 31, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013
			Marcellus Interest in Gas Gathering Systems [Member]	Marcellus Interest in Gas Gathering Systems [Member]	Mont Belvieu Joint Venture [Member]	Mont Belvieu Joint Venture [Member]	Moxa Oil and Gas Properties [Member]	Moxa Oil and Gas Properties [Member]	Intrastate Pipeline in Wyoming [Member]	Intrastate Pipeline in Wyoming [Member]
			Western Gas Partners, LP [Member]	Western Gas Partners, LP [Member]	Western Gas Partners, LP [Member]	Western Gas Partners, LP [Member]			Western Gas Partners, LP [Member]	Western Gas Partners, LP [Member]
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'	'	'
Date of acquisition agreement	'	'	'	31-Mar-13	'	30-Jun-13	'	31-Aug-13	'	30-Sep-13
Ownership interest purchased	'	'	33.75%	'	25.00%	'	'	'	'	'
Purchase price	$473	$0	$135	'	$78	'	$310	'	$28	'
Fair value, oil and gas properties acquired	'	'	'	'	'	'	$306	'	'	'

Acquisitions_and_Divestitures_1

Acquisitions and Divestitures - Divestitures (Detail) (USD $)	9 Months Ended		3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
			Mozambique Offshore Area 1 [Member]
Gain (Loss) on Disposition of Assets [Abstract]	'	'	'
Proceeds from divestitures	$451,000,000	$440,000,000	'
Net gains on divestitures	165,000,000	-23,000,000	'
Property, Plant and Equipment [Line Items]	'	'	'
Expected working interest sold	'	'	10.00%
Expected proceeds from divestiture	'	'	$2,640,000,000

Impairments_Impairments_by_Seg

Impairments - Impairments by Segment Table (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Impaired Long Lived Assets Held and Used [Line Items]	'	'	'	'
Impairments	$593	$4	$632	$166
Oil and Gas Exploration and Production Reporting Segment [Member]	'	'	'	'
Impaired Long Lived Assets Held and Used [Line Items]	'	'	'	'
Cost-method investment	0	1	10	12
Oil and Gas Exploration and Production Reporting Segment [Member] | U.S. Onshore Properties [Member]	'	'	'	'
Impaired Long Lived Assets Held and Used [Line Items]	'	'	'	'
Long-lived assets held for use	0	2	0	81
Oil and Gas Exploration and Production Reporting Segment [Member] | Gulf of Mexico Properties [Member]	'	'	'	'
Impaired Long Lived Assets Held and Used [Line Items]	'	'	'	'
Long-lived assets held for use	593	0	593	67
Midstream Reporting Segment [Member]	'	'	'	'
Impaired Long Lived Assets Held and Used [Line Items]	'	'	'	'
Long-lived assets held for use	$0	$1	$29	$6

Impairments_FairValue_Measurem

Impairments - Fair-Value Measurements Table (Detail) (Nonrecurring [Member], USD $)	Sep. 30, 2013		Sep. 30, 2012
In Millions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Long-lived assets held for use	$266		$38
Cost-method investment	32	[1]	34	[1]
Fair Value, Inputs, Level 1 [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Long-lived assets held for use	0		0
Cost-method investment	0		0
Fair Value, Inputs, Level 2 [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Long-lived assets held for use	0		0
Cost-method investment	0		0
Fair Value, Inputs, Level 3 [Member] | Income Approach Valuation Technique [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Long-lived assets held for use	266	[2]	38	[2]
Cost-method investment	$32	[1],[2]	$34	[1],[2]
[1]	This represents the Company’s after-tax net investment.
[2]	The income approach was used to measure fair value.

Suspended_Exploratory_Well_Cos1

Suspended Exploratory Well Costs (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013
			Greater Than One Year [Member]
Capitalized Exploratory Well Costs [Abstract]	'	'	'
Suspended exploratory well costs	$2,200,000,000	$2,100,000,000	'
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]	'	'	'
Exploratory well costs previously capitalized as suspended exploratory well costs for greater than one year at December 31, 2012, charged to dry hole expense	'	'	$95,000,000

Noncontrolling_Interests_Detai

Noncontrolling Interests (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Noncontrolling Interest [Line Items]	'	'
Net proceeds raised from offering by subsidiary	$418	$212
Western Gas Equity Partners, LP [Member] | Limited Partner [Member]	'	'
Noncontrolling Interest [Line Items]	'	'
Ownership interest in subsidiary	91.00%	'
Western Gas Partners, LP [Member]	'	'
Noncontrolling Interest [Line Items]	'	'
Common units issued to the public	7	'
Net proceeds raised from offering by subsidiary	$419	'
Western Gas Partners, LP [Member] | Limited Partner [Member] | Western Gas Equity Partners, LP, Ownership Interest [Member]	'	'
Noncontrolling Interest [Line Items]	'	'
Ownership interest in subsidiary	43.10%	'
Western Gas Partners, LP [Member] | Limited Partner [Member] | Other Anadarko Subsidiary, Ownership Interest [Member]	'	'
Noncontrolling Interest [Line Items]	'	'
Ownership interest in subsidiary	0.40%	'
Western Gas Partners, LP [Member] | General Partner [Member] | Western Gas Equity Partners, LP, Ownership Interest [Member]	'	'
Noncontrolling Interest [Line Items]	'	'
Ownership interest in subsidiary	2.00%	'

Derivative_Instruments_Additio

Derivative Instruments - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
	Mcf	Mcf
Derivative [Line Items]	'	'
Gross derivative liability	1,011,000,000	1,419,000,000
Aggregate fair value of derivative instruments with credit-risk-related contingent features for which a net liability position existed, net of collateral	52,000,000	94,000,000
Five Billion Dollar Facility [Member]	'	'
Derivative [Line Items]	'	'
Five billion dollar facility	5,000,000,000	'
Permitted to Offset Gross Derivative Asset with Financial Institutions [Member]	'	'
Derivative [Line Items]	'	'
Gross derivative liability	305,000,000	339,000,000
Securing most derivative counterparties [Member] | Five Billion Dollar Facility [Member]	'	'
Derivative [Line Items]	'	'
Five billion dollar facility	5,000,000,000	'
Commodity [Member] | Natural Gas [Member]	'	'
Derivative [Line Items]	'	'
Fixed-price physical transactions	10,000,000	10,000,000
Fixed-to-floating derivative transaction	10,000,000	10,000,000

Derivative_Instruments_Natural

Derivative Instruments - Natural Gas Production/Processing Derivative Activities Table (Detail) (Price Risk Derivative [Member], Natural Gas [Member], Not Designated as Hedging Instrument [Member])	9 Months Ended
	Sep. 30, 2013
April 2013 to October 2013 Settlement [Member] | Two Way Collars [Member]	'
Derivative [Line Items]	'
Derivative nonmonetary notional amount per day	600,000	[1]
April 2013 to October 2013 Settlement [Member] | Two Way Collars [Member] | Call Option [Member] | Short [Member]	'
Average price per MMBtu	'
Average ceiling price	4
April 2013 to October 2013 Settlement [Member] | Two Way Collars [Member] | Put Option [Member] | Long [Member]	'
Average price per MMBtu	'
Average floor price	3.18
2013 Settlement [Member] | Three-Way Collars [Member] | Offsetting Purchased and Sold Positions For Four Hundred Fifty Thousand Million British Thermal Units Per Day [Member]	'
Derivative [Line Items]	'
Derivative nonmonetary notional amount per day	0	[2]
2013 Settlement [Member] | Three-Way Collars [Member] | Call Option [Member] | Short [Member] | Offsetting Purchased and Sold Positions For Four Hundred Fifty Thousand Million British Thermal Units Per Day [Member]	'
Derivative [Line Items]	'
Derivative nonmonetary notional amount per day	450,000
2013 Settlement [Member] | Three-Way Collars [Member] | Call Option [Member] | Long [Member] | Offsetting Purchased and Sold Positions For Four Hundred Fifty Thousand Million British Thermal Units Per Day [Member]	'
Derivative [Line Items]	'
Derivative nonmonetary notional amount per day	-450,000
2013 Settlement [Member] | Fixed-Price Contracts [Member]	'
Derivative [Line Items]	'
Derivative nonmonetary notional amount per day	1,185,000
Average price per MMBtu	'
Average price per MMBtu	4
2014 Settlement [Member] | Three-Way Collars [Member]	'
Derivative [Line Items]	'
Derivative nonmonetary notional amount per day	600,000
2014 Settlement [Member] | Three-Way Collars [Member] | Call Option [Member] | Short [Member]	'
Average price per MMBtu	'
Average ceiling price	5.01
2014 Settlement [Member] | Three-Way Collars [Member] | Put Option [Member] | Short [Member]	'
Average price per MMBtu	'
Average floor price	2.75
2014 Settlement [Member] | Three-Way Collars [Member] | Put Option [Member] | Long [Member]	'
Average price per MMBtu	'
Average floor price	3.75
2014 Settlement [Member] | Fixed-Price Contracts [Member]	'
Derivative [Line Items]	'
Derivative nonmonetary notional amount per day	600,000
Average price per MMBtu	'
Average price per MMBtu	4.26
[1]	The two-way collars have a contract term of April 2013 to October 2013.
[2]	The Company entered into offsetting purchased and sold natural-gas three-way collars of 450,000 MMBtu/d for 2013 settlement.

Derivative_Instruments_Crude_O

Derivative Instruments - Crude Oil Production/Processing Derivative Activities Table (Detail) (Not Designated as Hedging Instrument [Member], 2013 Settlement [Member], Crude Oil [Member], Price Risk Derivative [Member])	9 Months Ended
	Sep. 30, 2013
Three-Way Collars [Member]	'
Derivative [Line Items]	'
Derivative nonmonetary notional amount per day	26
Three-Way Collars [Member] | Call Option [Member] | Short [Member]	'
Average price per barrel	'
Average ceiling price	125.15
Three-Way Collars [Member] | Put Option [Member] | Short [Member]	'
Average price per barrel	'
Average floor price	85
Three-Way Collars [Member] | Put Option [Member] | Long [Member]	'
Average price per barrel	'
Average floor price	105
Fixed-Price Contracts [Member]	'
Derivative [Line Items]	'
Derivative nonmonetary notional amount per day	167
Average price per barrel	'
Average price per barrel	102.74

Derivative_Instruments_Interes

Derivative Instruments - Interest-Rate Derivatives Table (Detail) (Not Designated as Hedging Instrument [Member], USD $)	9 Months Ended
	Sep. 30, 2013
Interest-Rate Swap 1 [Member]	'
Derivative [Line Items]	'
Notional principal amount of interest-rate swap	750,000,000
Weighted-average interest rate for interest-rate swap	6.00%
Interest-Rate Swap 1 [Member] | Minimum [Member]	'
Derivative [Line Items]	'
Reference period for interest-rate swap	1-Jun-14
Interest-Rate Swap 1 [Member] | Maximum [Member]	'
Derivative [Line Items]	'
Reference period for interest-rate swap	1-Jun-24
Interest-Rate Swap 2 [Member]	'
Derivative [Line Items]	'
Notional principal amount of interest-rate swap	1,100,000,000
Weighted-average interest rate for interest-rate swap	5.57%
Interest-Rate Swap 2 [Member] | Minimum [Member]	'
Derivative [Line Items]	'
Reference period for interest-rate swap	1-Jun-14
Interest-Rate Swap 2 [Member] | Maximum [Member]	'
Derivative [Line Items]	'
Reference period for interest-rate swap	1-Jun-44
Interest-Rate Swap 3 [Member]	'
Derivative [Line Items]	'
Notional principal amount of interest-rate swap	50,000,000
Weighted-average interest rate for interest-rate swap	5.91%
Interest-Rate Swap 3 [Member] | Minimum [Member]	'
Derivative [Line Items]	'
Reference period for interest-rate swap	1-Sep-16
Interest-Rate Swap 3 [Member] | Maximum [Member]	'
Derivative [Line Items]	'
Reference period for interest-rate swap	1-Sep-26
Interest-Rate Swap 4 [Member]	'
Derivative [Line Items]	'
Notional principal amount of interest-rate swap	750,000,000
Weighted-average interest rate for interest-rate swap	5.86%
Interest-Rate Swap 4 [Member] | Minimum [Member]	'
Derivative [Line Items]	'
Reference period for interest-rate swap	1-Sep-16
Interest-Rate Swap 4 [Member] | Maximum [Member]	'
Derivative [Line Items]	'
Reference period for interest-rate swap	1-Sep-46

Derivative_Instruments_Effect_

Derivative Instruments - Effect of Derivative Instruments - Balance Sheet Table (Detail) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Derivatives Fair Value [Line Items]	'		'
Gross derivative assets	$457		$506
Gross derivative liabilities	-1,011		-1,419
Commodity Derivatives [Member]	'		'
Derivatives Fair Value [Line Items]	'		'
Gross derivative assets	457		506
Gross derivative liabilities	-246		-225
Commodity Derivatives [Member] | Other Current Assets [Member]	'		'
Derivatives Fair Value [Line Items]	'		'
Gross derivative assets	359		475
Gross derivative liabilities	-170		-197
Commodity Derivatives [Member] | Other Noncurrent Assets [Member]	'		'
Derivatives Fair Value [Line Items]	'		'
Gross derivative assets	50		24
Gross derivative liabilities	-13		-7
Commodity Derivatives [Member] | Accrued Expenses [Member]	'		'
Derivatives Fair Value [Line Items]	'		'
Gross derivative assets	48		6
Gross derivative liabilities	-61		-14
Commodity Derivatives [Member] | Other Liabilities [Member]	'		'
Derivatives Fair Value [Line Items]	'		'
Gross derivative assets	0		1
Gross derivative liabilities	-2		-7
Interest-Rate and Other Derivatives [Member]	'		'
Derivatives Fair Value [Line Items]	'		'
Gross derivative assets	0		0
Gross derivative liabilities	-765		-1,194
Interest-Rate and Other Derivatives [Member] | Accrued Expenses [Member]	'		'
Derivatives Fair Value [Line Items]	'		'
Gross derivative assets	0		0
Gross derivative liabilities	-550	[1]	0
Interest-Rate and Other Derivatives [Member] | Other Liabilities [Member]	'		'
Derivatives Fair Value [Line Items]	'		'
Gross derivative assets	0		0
Gross derivative liabilities	($215)	[1]	($1,194)	[1]
[1]	Interest-rate swaps with June 2014 maturity dates were reclassified from other liabilities to accrued expenses during the second quarter of 2013.

Derivative_Instruments_Effect_1

Derivative Instruments - Effect of Derivative Instruments - Statement of Income Table (Detail) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Derivative [Line Items]	'		'		'		'
Unrealized (gains) losses on derivatives, net	'		'		($359)		$539
Total (gains) losses on derivatives, net	72		251		-393		-77
Gathering, Processing, and Marketing Sales and Gains (Losses) on Derivatives, Net [Member]	'		'		'		'
Derivative [Line Items]	'		'		'		'
Realized (gains) losses on derivatives, net	28		-197		-37		-598
Unrealized (gains) losses on derivatives, net	36		456		-359		539
Total (gains) losses on derivatives, net	64		259		-396		-59
Commodity Derivatives [Member] | Gathering, Processing, and Marketing Sales [Member]	'		'		'		'
Derivative [Line Items]	'		'		'		'
Realized (gains) losses on derivatives, net	2	[1]	3	[1]	9	[1]	0	[1]
Unrealized (gains) losses on derivatives, net	-10	[1]	5	[1]	-12	[1]	18	[1]
Total (gains) losses on derivatives, net	-8	[1]	8	[1]	-3	[1]	18	[1]
Commodity Derivatives [Member] | (Gains) Losses on Derivatives, net [Member]	'		'		'		'
Derivative [Line Items]	'		'		'		'
Realized (gains) losses on derivatives, net	26		-200		-46		-600
Unrealized (gains) losses on derivatives, net	120		437		81		369
Total (gains) losses on derivatives, net	146		237		35		-231
Interest-Rate and Other Derivatives [Member] | (Gains) Losses on Derivatives, net [Member]	'		'		'		'
Derivative [Line Items]	'		'		'		'
Realized (gains) losses on derivatives, net	0		0		0		2
Unrealized (gains) losses on derivatives, net	-74		14		-428		152
Total (gains) losses on derivatives, net	($74)		$14		($428)		$154
[1]	Represents the effect of marketing and trading derivative activities.

Derivative_Instruments_Fair_Va

Derivative Instruments - Fair Value Table (Detail) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	$457		$506
Gross derivative liabilities	-1,011		-1,419
Derivative assets netting	-232	[1]	-211	[1]
Derivative liabilities netting	232	[1]	211	[1]
Cash collateral from counterparties	-1		0
Cash collateral held by counterparties	1		1
Derivative assets	224		295
Derivative liabilities	-778		-1,207
Commodity Derivatives [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	457		506
Gross derivative liabilities	-246		-225
Interest-Rate and Other Derivatives [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	0		0
Gross derivative liabilities	-765		-1,194
Derivative liabilities netting	0	[1]	0	[1]
Cash collateral held by counterparties	0		0
Derivative liabilities	-765		-1,194
Financial Institutions [Member] | Commodity Derivatives [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Derivative assets netting	-226	[1]	-206	[1]
Derivative liabilities netting	226	[1]	206	[1]
Cash collateral from counterparties	-1		0
Cash collateral held by counterparties	1		1
Derivative assets	156		253
Derivative liabilities	-9		-1
Other Counterparties [Member] | Commodity Derivatives [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Derivative assets netting	-6	[1]	-5	[1]
Derivative liabilities netting	6	[1]	5	[1]
Cash collateral from counterparties	0		0
Cash collateral held by counterparties	0		0
Derivative assets	68		42
Derivative liabilities	-4		-12
Fair Value, Inputs, Level 1 [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	4		6
Gross derivative liabilities	-4		-6
Fair Value, Inputs, Level 1 [Member] | Interest-Rate and Other Derivatives [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative liabilities	0		0
Fair Value, Inputs, Level 1 [Member] | Financial Institutions [Member] | Commodity Derivatives [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	4		6
Gross derivative liabilities	-4		-6
Fair Value, Inputs, Level 1 [Member] | Other Counterparties [Member] | Commodity Derivatives [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	0		0
Gross derivative liabilities	0		0
Fair Value, Inputs, Level 2 [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	453		500
Gross derivative liabilities	-1,007		-1,413
Fair Value, Inputs, Level 2 [Member] | Interest-Rate and Other Derivatives [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative liabilities	-765		-1,194
Fair Value, Inputs, Level 2 [Member] | Financial Institutions [Member] | Commodity Derivatives [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	379		453
Gross derivative liabilities	-232		-202
Fair Value, Inputs, Level 2 [Member] | Other Counterparties [Member] | Commodity Derivatives [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	74		47
Gross derivative liabilities	-10		-17
Fair Value, Inputs, Level 3 [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	0		0
Gross derivative liabilities	0		0
Fair Value, Inputs, Level 3 [Member] | Interest-Rate and Other Derivatives [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative liabilities	0		0
Fair Value, Inputs, Level 3 [Member] | Financial Institutions [Member] | Commodity Derivatives [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	0		0
Gross derivative liabilities	0		0
Fair Value, Inputs, Level 3 [Member] | Other Counterparties [Member] | Commodity Derivatives [Member] | Recurring [Member]	'		'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'
Gross derivative assets	0		0
Gross derivative liabilities	$0		$0
[1]	Represents the impact of netting commodity derivative assets and liabilities with counterparties where the Company has the contractual right and intends to net settle.

Debt_and_Interest_Expense_Outs

Debt and Interest Expense - Outstanding Debt Table (Detail) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Debt Disclosure [Abstract]	'		'
Total debt at face value	$15,302		$14,952
Net unamortized discounts and premiums (1)	-1,655	[1]	-1,683	[1]
Total long-term debt	$13,647		$13,269
[1]	Unamortized discounts and premiums are amortized over the term of the related debt.

Debt_and_Interest_Expense_Addi

Debt and Interest Expense - Additional Information (Detail) (USD $)

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Oct. 10, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Fair Value Inputs Level 1 and Level 2 [Member]

Fair Value Inputs Level 1 and Level 2 [Member]

Senior Notes 1 [Member]

Senior Notes 2 [Member]

Senior Notes Zero Coupon [Member]

Senior Notes Zero Coupon [Member]

Senior Notes 3 [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Market Approach Valuation Technique [Member]

Market Approach Valuation Technique [Member]

Western Gas Partners, LP [Member]

Western Gas Partners, LP [Member]

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of credit, maximum capacity

'

'

'

'

'

'

'

'

'

'

'

$5,000,000,000

$800,000,000

Debt instrument, principal amount

15,302,000,000

'

'

14,952,000,000

'

'

500,000,000

275,000,000

'

'

250,000,000

'

'

Debt instrument, stated interest rate

'

'

'

'

'

'

7.63%

5.75%

'

'

2.60%

'

'

Debt instrument, maturity date

'

'

'

'

'

'

15-Mar-14

15-Jun-14

10-Oct-36

'

15-Aug-18

'

'

Debt instrument, accreted value

13,647,000,000

13,538,000,000

13,663,000,000

13,269,000,000

'

'

'

'

'

718,000,000

'

'

'

Debt Instrument, earliest call date

'

'

'

'

'

'

'

'

10-Oct-13

'

'

'

'

Estimated fair value of total borrowings

'

'

'

'

15,800,000,000

16,200,000,000

'

'

'

'

'

'

'

Line of credit, expiration date

'

'

'

'

'

'

'

'

'

'

'

'

24-Mar-16

Line of credit, outstanding borrowings

'

'

'

'

'

'

'

'

'

'

'

'

100,000,000

Line of credit, interest rate

'

'

'

'

'

'

'

'

'

'

'

'

1.68%

Line of credit, available borrowing capacity

'

'

'

'

'

'

'

'

'

'

'

'

687,000,000

Outstanding letters of credit

'

'

'

'

'

'

'

'

'

'

'

'

$13,000,000

Debt_and_Interest_Expense_Debt

Debt and Interest Expense - Debt Activity Table (Detail) (USD $)	3 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013
Debt Disclosure [Abstract]	'	'	'
Carrying value, beginning balance	$13,538,000,000	$13,663,000,000	$13,269,000,000
Debt Instrument [Line Items]	'	'	'
Other, net	9,000,000	10,000,000	9,000,000
Carrying value, ending balance	13,647,000,000	13,538,000,000	13,663,000,000
Western Gas Partners, LP [Member] | Senior Notes 3 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Issuance	250,000,000	'	'
Western Gas Partners, LP [Member] | Revolving Credit Facility [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Borrowings	100,000,000	110,000,000	385,000,000
Repayments	($250,000,000)	($245,000,000)	'

Debt_and_Interest_Expense_Inte

Debt and Interest Expense - Interest Expense Table (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Interest Expense [Abstract]	'	'	'	'
Current debt, long-term debt, and other	$240	$238	$710	$724
Capitalized interest	-63	-53	-197	-163
Interest expense	$177	$185	$513	$561

Stockholders_Equity_Detail

Stockholders' Equity (Detail) (USD $)	3 Months Ended				9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Net income (loss)	'		'		'		'
Net income (loss) attributable to common stockholders	$182		$121		$1,571		$2,188
Less distributions on participating securities	0		0		1		1
Less undistributed income allocated to participating securities	1		1		9		13
Basic	181		120		1,561		2,174
Diluted	$181		$120		$1,561		$2,174
Shares	'		'		'		'
Average number of common shares outstanding—basic	503		500		502		499
Dilutive effect of stock options	2		2		2		2
Average number of common shares outstanding—diluted	505		502		504		501
Excluded (1)	3	[1]	6	[1]	4	[1]	6	[1]
Net income (loss) per common share	'		'		'		'
Basic	$0.36		$0.24		$3.11		$4.35
Diluted	$0.36		$0.24		$3.10		$4.34
Dividends per common share	$0.18		$0.09		$0.36		$0.27
[1]	Inclusion of certain shares would have had an anti-dilutive effect.

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]	'
Balance at December 31, 2012	($640)
Reclassifications to Consolidated Statement of Income	62
Balance at September 30, 2013	-578
Interest-rate Derivatives Previously Subject to Hedge Accounting [Member]	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'
Balance at December 31, 2012	-61
Reclassifications to Consolidated Statement of Income	5
Balance at September 30, 2013	-56
Pension and Other Postretirement Plans [Member]	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'
Balance at December 31, 2012	-579
Reclassifications to Consolidated Statement of Income	57
Balance at September 30, 2013	($522)

Commitments_Detail

Commitments (Detail) (Deepwater Drillship [Member], USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Deepwater Drillship [Member]	'
Operating Leased Assets [Line Items]	'
Operating lease, period	'3 years
Total future minimum lease payments	$464
Aggregate future annual minimum lease payments in 2014	33
Aggregate future annual minimum lease payments in 2015	154
Aggregate future annual minimum lease payments in 2016	155
Aggregate future annual minimum lease payments in 2017	$122

Contingencies_Detail

Contingencies (Detail) (USD $)	3 Months Ended		9 Months Ended					9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2011	Sep. 30, 2013	Sep. 30, 2013
	Tronox Litigation [Member]	Tronox Litigation [Member]	Tronox Litigation [Member]	Tronox Litigation [Member]	Tronox Litigation [Member]	Macondo Exploration Well [Member]	Deepwater Horizon [Member]	Third Party Bankruptcy Assignment [Member]
					Principal Portion of Maximum Loss Range [Member]		BP indemnification liability [Member]
Loss Contingencies [Line Items]	'	'	'	'	'	'	'	'
Anadarko's nonoperated interest	'	'	'	'	'	25.00%	'	'
Loss contingency accrual at carrying value	$0	'	$0	'	'	'	$0	'
Damages sought, including interest, in excess of	'	'	18,900,000,000	'	'	'	'	'
Range of potential loss, minimum	0	'	0	'	'	'	'	'
Range of potential loss, maximum	1,400,000,000	'	1,400,000,000	'	985,000,000	'	'	'
Pretax loss	0	0	0	-250,000,000	'	'	'	131,000,000
Decommissioning obligations included in accrued expenses	'	'	'	'	'	'	'	44,000,000
Decommissioning obligations included in other long-term liabilities	'	'	'	'	'	'	'	$85,000,000

Income_Taxes_Income_Tax_Expens

Income Taxes - Income Tax Expense (Benefit) Table (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Effective Income Tax Rate Reconciliation, Amount [Abstract]	'	'	'	'
Income tax expense (benefit)	$240	$248	$1,263	$764
Effective tax rate	52.00%	64.00%	43.00%	25.00%

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Abstract]	'	'	'	'
U.S. federal statutory rate	35.00%	35.00%	35.00%	35.00%

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash paid (received)	'	'
Interest	$569	$613
Income taxes	137	-13
Non-cash investing activities	'	'
Fair value of properties and equipment received in non-cash exchange transactions	$13	$65

Segment_Information_Additional

Segment Information - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
	Segment
Segment Reporting [Abstract]	'
Number of reporting segments	3
Midstream Reporting Segment [Member]	'
Segment Reporting Information [Line Items]	'
Number of operating segments	2

Segment_Information_Reconcilia

Segment Information - Reconciliation of Consolidated Adjusted EBITDAX to Income (Loss) before Income Taxes Table (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]	'	'	'	'
Income (loss) before income taxes	$463	$390	$2,929	$3,019
Exploration expense	272	297	714	1,662
DD&A	996	979	2,958	2,936
Impairments	593	4	632	166
Interest expense	177	185	513	561
Deepwater Horizon settlement and related costs	5	4	12	15
Algeria exceptional profits tax settlement	0	7	33	-1,797
Segment Reporting Information [Line Items]	'	'	'	'
Unrealized (gains) losses on derivatives, net	'	'	-359	539
Certain other nonoperating items	'	'	0	-250
Less net income attributable to noncontrolling interests	41	21	95	67
Consolidated Adjusted EBITDAX	2,491	2,301	7,412	6,786
Certain Other Nonoperating Items [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Certain other nonoperating items	-10	0	75	0
Gathering, Processing, and Marketing Sales and Gains (Losses) on Derivatives, Net [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Unrealized (gains) losses on derivatives, net	36	456	-359	539
Realized (gains) losses on interest-rate and other derivatives, net	28	-197	-37	-598
(Gains) Losses on Derivatives, net [Member] | Interest-Rate and Other Derivatives [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Unrealized (gains) losses on derivatives, net	-74	14	-428	152
Realized (gains) losses on interest-rate and other derivatives, net	0	0	0	2
Tronox Litigation [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Tronox-related contingent loss	$0	$0	$0	($250)

Segment_Information_Selected_F

Segment Information - Selected Financial Information for Anadarko's Reporting Segments Table (Detail) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Segment Reporting Information [Line Items]	'		'		'		'
Revenue	$3,789		$3,283		$10,947		$9,895
Gains (losses) on divestitures and other, net	64		49		296		106
Total	3,853		3,332		11,243		10,001
Operating costs and expenses (1)	1,298	[1]	1,225	[1]	3,776	[1]	3,780	[1]
Other (income) expense, net	-23		-10		69		-264
Net income attributable to noncontrolling interests	41		21		95		67
Total expenses and other	1,352		1,036		3,819		3,233
Unrealized (gains) losses on derivatives, net included in marketing revenue	'		'		-359		539
Adjusted EBITDAX	2,491		2,301		7,412		6,786
Other and Intersegment Eliminations [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenue	-174		-137		-475		-396
Gains (losses) on divestitures and other, net	57		43		284		131
Total	-117		-94		-191		-265
Operating costs and expenses (1)	-12	[1]	51	[1]	15	[1]	132	[1]
Total expenses and other	1		-159		-37		-482
Adjusted EBITDAX	-118		65		-154		217
Gathering, Processing, and Marketing Sales [Member] | Commodity Contract [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Realized (gains) losses on derivatives, net	2	[2]	3	[2]	9	[2]	0	[2]
Unrealized (gains) losses on derivatives, net included in marketing revenue	-10	[2]	5	[2]	-12	[2]	18	[2]
(Gains) Losses on Derivatives, net [Member] | Commodity Contract [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Realized (gains) losses on derivatives, net	26		-200		-46		-600
Unrealized (gains) losses on derivatives, net included in marketing revenue	120		437		81		369
(Gains) Losses on Derivatives, net [Member] | Commodity Contract [Member] | Other and Intersegment Eliminations [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Realized (gains) losses on derivatives, net	26		-200		-46		-600
Excluding Certain Other Nonoperating Items [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Other (income) expense, net	-13	[3]	-10	[3]	-6	[3]	-14	[3]
Excluding Certain Other Nonoperating Items [Member] | Other and Intersegment Eliminations [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Other (income) expense, net	-13	[3]	-10	[3]	-6	[3]	-14	[3]
Oil and Gas Exploration and Production Reporting Segment [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenue	1,916		1,393		5,044		5,180
Gains (losses) on divestitures and other, net	7		12		12		-17
Oil and Gas Exploration and Production Reporting Segment [Member] | Operating Segments [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Total	3,439		2,992		9,960		8,959
Operating costs and expenses (1)	930	[1]	840	[1]	2,656	[1]	2,639	[1]
Total expenses and other	930		840		2,656		2,639
Adjusted EBITDAX	2,509		2,152		7,304		6,320
Oil and Gas Exploration and Production Reporting Segment [Member] | Intersegment Revenues [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenue	1,516		1,587		4,904		3,796
Midstream Reporting Segment [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenue	95		80		267		248
Gains (losses) on divestitures and other, net	0		-6		0		-8
Midstream Reporting Segment [Member] | Operating Segments [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Total	382		306		1,072		941
Operating costs and expenses (1)	216	[1]	182	[1]	613	[1]	545	[1]
Net income attributable to noncontrolling interests	41		21		95		67
Total expenses and other	257		203		708		612
Adjusted EBITDAX	125		103		364		329
Midstream Reporting Segment [Member] | Intersegment Revenues [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenue	287		232		805		701
Marketing Reporting Segment [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenue	1,778		1,810		5,636		4,467
Gains (losses) on divestitures and other, net	0		0		0		0
Marketing Reporting Segment [Member] | Operating Segments [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Total	149		128		402		366
Operating costs and expenses (1)	164	[1]	152	[1]	492	[1]	464	[1]
Total expenses and other	164		152		492		464
Adjusted EBITDAX	-25		-19		-102		-80
Marketing Reporting Segment [Member] | Intersegment Revenues [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenue	-1,629		-1,682		-5,234		-4,101
Marketing Reporting Segment [Member] | Gathering, Processing, and Marketing Sales [Member] | Commodity Contract [Member] | Operating Segments [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Unrealized (gains) losses on derivatives, net included in marketing revenue	($10)		$5		($12)		$18
[1]	Operating costs and expenses excludes exploration expense, DD&A, impairments, Deepwater Horizon settlement and related costs, and Algeria exceptional profits tax settlement since these expenses are excluded from Adjusted EBITDAX.
[2]	Represents the effect of marketing and trading derivative activities.
[3]	Other (income) expense, net excludes Tronox-related contingent loss and certain other nonoperating items since these expenses are excluded from Adjusted EBITDAX.

Pension_Plans_and_Other_Postre2

Pension Plans and Other Postretirement Benefits (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension Plans, Defined Benefit [Member]	'	'	'	'
Components of net periodic benefit cost	'	'	'	'
Service cost	$21	$19	$64	$57
Interest cost	19	21	58	64
Expected return on plan assets	-22	-23	-68	-68
Amortization of net actuarial loss (gain)	29	23	88	69
Amortization of net prior service cost (credit)	0	0	0	0
Net periodic benefit cost	47	40	142	122
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'	'	'
Components of net periodic benefit cost	'	'	'	'
Service cost	2	2	7	7
Interest cost	3	4	10	12
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss (gain)	0	0	0	0
Amortization of net prior service cost (credit)	1	0	1	1
Net periodic benefit cost	$6	$6	$18	$20

Pension_Plans_and_Other_Postre3

Pension Plans and Other Postretirement Benefits Pension Plans and Other Postretirement Benefits - Additional Information (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Pension Plans, Defined Benefit [Member] | Funded Plans Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Employer Contributions	$122
Expected employer contributions during the remainder of the current fiscal year	2
Pension Plans, Defined Benefit [Member] | Unfunded Plans Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Employer Contributions	6
Expected employer contributions during the remainder of the current fiscal year	30
Other Postretirement Benefit Plans, Defined Benefit [Member] | Unfunded Plans Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Employer Contributions	11
Expected employer contributions during the remainder of the current fiscal year	$5