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Commitments - Additional Information (Detail) (USD $)	9 Months Ended	18 Months Ended	11 Months Ended
Commitments - Additional Information (Detail) (USD $)	Sep. 30, 2011 Drilling rigs commitment [Member]	Oct. 16, 2011 Deepwater Horizon [Member] Operating Agreement [Member] BP Exploration and Production Inc. [Member]	Nov. 30, 2011 Deepwater Horizon [Member] BP Settlement Agreement [Member]
Operating Leased Assets [Line Items]
Operating leases, period	5 years
Operating lease obligations	$ 1,200,000,000
Operating leases, future minimum payment, due in 2013	30,000,000
Operating leases, future minimum payment, due in 2014	209,000,000
Operating leases, future minimum payment, due in 2015	238,000,000
Operating leases, future minimum payments, due thereafter	715,000,000
Loss Contingencies [Line Items]
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