Contingencies - Deepwater Horizon Events (Detail) (USD $)						12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 BP indemnification liability [Member]	Sep. 30, 2011 Macondo Exploration Well [Member]	Feb. 19, 2013 Deepwater Horizon [Member]	Dec. 31, 2011 Deepwater Horizon [Member] BP Settlement Agreement [Member]	Dec. 31, 2012 Deepwater Horizon [Member] Oil Pollution Act of 1990 [Member]	Feb. 05, 2013 Deepwater Horizon [Member] Oil Pollution Act of 1990 [Member] BP Exploration and Production Inc. [Member]	Dec. 31, 2012 Deepwater Horizon [Member] BP indemnification liability [Member]
Loss Contingencies [Line Items]
Anadarko's non-operated interest				25.00%
Cash payment for Deepwater Horizon settlement						$ 4,000,000,000
Loss contingency accrual at carrying value	49,000,000	342,000,000							0
Gross OPA-related environmental costs, excluding amounts BP has already funded, amounts that cannot reasonably be estimated by BP, non-OPA-related fines and penalties, and estimated state and local governmental claims								10,700,000,000
Allocable percentage share of gross OPA-related environmental costs							0.00%
Accrual for environmental loss contingencies	81,000,000	92,000,000					0
Penalties or fines assessed against the Company					$ 0