Commitments and Contingencies (Details) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended				1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	3 Months Ended		1 Months Ended
	Oct. 31, 2012 Macondo well incident Plaintiff_Claim	Aug. 02, 2010 Macondo well incident bbl	Dec. 31, 2012 Macondo well incident Phase Decendent Louisiana_Parish Mexican_State Allegedly_Injured_Person Party Independent_Bureau Complaint Personal_Injury_Lawsuit	Apr. 18, 2012 Macondo well incident Settlement_Agreement	Apr. 22, 2010 Macondo well incident Fatality	Mar. 31, 2012 Macondo well incident Corporate and other	Nov. 30, 2012 Macondo well incident BP Exploration Criminal_Charge Monitor	Dec. 31, 2012 Macondo well incident BP Exploration	Jan. 31, 2013 Macondo well incident Transocean Subsequent Event Misdemeanor	Dec. 31, 2012 Macondo well incident Transocean Subsequent Event	Sep. 30, 2011 Barracuda-Caratinga arbitration	Dec. 31, 2012 Barracuda-Caratinga arbitration	Jan. 31, 2013 Barracuda-Caratinga arbitration Subsequent Event	Dec. 31, 2012 Securities and related litigation Class_Action
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 criminal charges							14
Number of criminal charges from negligent misinterpretation of negative- pressure test							13
Amount agreed to pay related to legal matter							4,000,000,000		1,000,000,000
Criminal fines							1,300,000,000		400,000,000
Probation term								5 years		5 years
Number of monitors							2
Monitor term								4 years
Number of misdemeanor violations									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
Litigation [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			10
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 hundredths)			10.00%
BPs estimated cost of settlement agreement with PSC								8,500,000,000
Number of settlement agreements				2
Petrobras arbitration claim against KBR												220,000,000
Arbitration award issued against KBR											201,000,000
Payment made for KBR obligation													219,000,000
Number of similar class action lawsuits that were later consolidated into one suit														20
Indemnification and insurance [Abstract]
Total amount of general liability insurance program			600,000,000
Legal fees			175,000,000
Legal fees and related expenses covered by insurance			158,000,000
Pre-tax charge recognized by BP as a result of the Macondo well incident			$ 40,000,000,000
TypesOfPlaintiffClaimsDismissed	3