Commitments and Contingencies (Details) (USD $)	9 Months Ended
	Sep. 30, 2012 bbl Personal_Injury_Lawsuits Decendents Cement_Barrier Complaints Louisiana_Parishes Mexican_States Allegedly_Injured_Persons Phases Parties Independent_Bureaus Key_Findings Pod General_Root_Causes Centralizers	Apr. 18, 2012 Settlement_Agreements	Mar. 31, 2012	Apr. 22, 2010 Fatalities
Macondo well incident
Loss Contingencies [Line Items]
Federal government estimate of oil discharged from the well (in barrels)	4,900,000
Number of fatalities				11
Loss contingency, estimate of possible loss			$ 300,000,000
Number of independent bureaus created to replace the Minerals Management Service	2
Number of parties-of-interest in the Marine Board investigation	16
Maximum per day assessment for negligent discharges under the CWA	50,000
Maximum per day assessment for knowing discharges under the CWA	100,000
Maximum assessment for knowing endangerment under the CWA	2,000,000
Maximum per barrel civil penalty for strict liability under the CWA	1,100
Maximum per barrel civil penalty for gross negligence under the CWA	4,300
Liability cap under the OPA in addition to the full cost of removal of the discharged oil	75,000,000
Maximum fine per bird killed under the MBTA	15,000
Maximum imprisonment under the MBTA (in months)	6 months
Maximum civil penalty per violation under the ESA	25,000
Maximum criminal penalty per violation under the ESA	50,000
Anadarko interest in Macondo well	25.00%
DOJ minimum estimate of removal costs and damages to the United Sates due to discharges of oil into the Gulf of Mexico	75,000,000
Number of key findings related to possible causes of the well incident	8
Number of safeguards that could have contained hydrocarbon pressures	3
Number of centralizers used by BP	6
Number of general root causes of the well incident identified by the Investigation Report	2
Number of pods with depleted battery	1
Number of cement barriers	1
Maximum per day fine for violating federal regulations related to INCs	35,000
Number of days to file notice after conclusion of MDL (in days)	15 days
Number of days to appeal INCs issued by the BSEE (in days)	60 days
Number of minutes taken to note loss of well control (in minutes)	50 minutes
Loss Contingency, Information about Litigation Matters [Abstract]
Minimum number of environmental class-action complaints	400
Minimum number of wrongful death and personal injury multiple plaintiff lawsuits	7
Number of decedents in personal injury lawsuits	4
Number of allegedly injured persons in personal injury lawsuits	11
Minimum number of lawsuits naming the company	6
Number of Mexican states included in pollution complaint	3
Number of Louisiana parishes included in pollution complaint	7
Number of phases involved in limitation action trial	2
Interest of MOEX in Macondo well (in hundreths)	10.00%
BPs estimated cost of settlement agreement with PSC	7,800,000,000
Number of settlement agreements		2
Indemnification and insurance [Abstract]
Total amount of general liability insurance program	600,000,000
Legal fees and related expenses covered by insurance	140,000,000
Pre-tax charge recognized by BP as a result of the Macondo well incident	40,000,000,000
Barracuda-Caratinga arbitration
Loss Contingency, Information about Litigation Matters [Abstract]
Petrobras arbitration claim against KBR	220,000,000
Arbitration award issued against KBR	$ 201,000,000
Securities and related litigation
Loss Contingency, Information about Litigation Matters [Abstract]
Number of similar class action lawsuits that were later consolidated into one suit	20
Shareholder derivative cases
Loss Contingency, Information about Litigation Matters [Abstract]
Number of shareholder derivative lawsuits	2