Deepwater Horizon Events - Background, Settlement, and BP Indemnification (Detail) (USD $)		18 Months Ended	12 Months Ended
Sep. 30, 2011 Macondo Exploration Well [Member]	Oct. 16, 2011 Deepwater Horizon [Member] Operating Agreement [Member] BP Exploration and Production Inc. [Member]	Dec. 31, 2011 Deepwater Horizon [Member] BP Settlement Agreement [Member]
Loss Contingencies [Line Items]
Percentage of Anadarko's holding of non-operating leasehold interest	25.00%
Payments for Deepwater Horizon settlement costs			$ 4,000,000,000
Amounts invoiced to Anadarko by BP for costs related to the Deepwater Horizon incident		$ 6,100,000,000

The amount of cash paid for the settlement of litigation or for other legal issues during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 27

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3536-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration