Derivative financial instruments - Fair value of hedge ineffectiveness (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Fair value hedges \| Interest rate risk on finance debt
Disclosure of detailed information about financial instruments [line items]
Change in fair value of hedging instrument used to calculate ineffectiveness	$ (70)
Change in fair value of hedged item used to calculate ineffectiveness	69
Hedge ineffectiveness recognized in profit or (loss)	(1)
Fair value hedges \| Interest rate and foreign currency risk on finance debt
Disclosure of detailed information about financial instruments [line items]
Change in fair value of hedging instrument used to calculate ineffectiveness	812
Change in fair value of hedged item used to calculate ineffectiveness	(809)
Hedge ineffectiveness recognized in profit or (loss)	3
Highly probable forecast capital expenditure \| Cash flow hedges \| Foreign exchange risk
Disclosure of detailed information about financial instruments [line items]
Change in fair value of hedging instrument used to calculate ineffectiveness	(5)
Change in fair value of hedged item used to calculate ineffectiveness	5
Hedge ineffectiveness recognized in profit or (loss)	0
Highly probable forecast sales \| Cash flow hedges \| Commodity price risk
Disclosure of detailed information about financial instruments [line items]
Change in fair value of hedging instrument used to calculate ineffectiveness	(126)
Change in fair value of hedged item used to calculate ineffectiveness	126
Hedge ineffectiveness recognized in profit or (loss)	$ 0

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfFinancialInstrumentsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The gain (loss) on the change in fair value of the hedged item used as a basis for recognising hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 24B
-Subparagraph a
-Clause iv
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_24B_a_iv&doctype=Standard
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 24B
-Subparagraph b
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_24B_b_i&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_GainLossOnChangeInFairValueOfHedgedItemUsedAsBasisForRecognisingHedgeIneffectiveness
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The gain (loss) on the change in fair value of the hedging instrument used as a basis for recognising hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 24A
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_24A_c&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_GainLossOnChangeInFairValueOfHedgingInstrumentUsedAsBasisForRecognisingHedgeIneffectiveness
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The gain (loss) recognised in profit or loss on hedge ineffectiveness. [Refer: Gain (loss) on hedge ineffectiveness]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 24C
-Subparagraph a
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_24C_a_i&doctype=Standard
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 24C
-Subparagraph b
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_24C_b_ii&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_GainLossOnHedgeIneffectivenessRecognisedInProfitOrLoss
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	ifrs-full_TypesOfHedgesAxis=ifrs-full_FairValueHedgesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfRisksAxis=ifrs-full_InterestRateRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfRisksAxis=bp_CurrencyAndInterestRateRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_HedgedItemsAxis=bp_HighlyProbableForecastCapitalExpenditureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfHedgesAxis=ifrs-full_CashFlowHedgesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfRisksAxis=ifrs-full_CurrencyRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_HedgedItemsAxis=bp_HighlyProbableForecastSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfRisksAxis=ifrs-full_CommodityPriceRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: