Cash Proceeds Received from Derivatives

No definition available.

Name:	mro_CashProceedsReceivedfromDerivatives
Namespace Prefix:	mro_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeInstrumentsGainLossLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Nominal number of units used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount before tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e689-108580

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 17A
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL34724391-108580

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative contract measured in volume but not the derivative contract itself.

+ References

No definition available.

+ Details

Name:	us-gaap_UnderlyingDerivativeVolume
Namespace Prefix:	us-gaap_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unrealized gain (loss) related to derivatives designated as cash flow hedging instruments, recorded in results of operations to the extent that the cash flow hedge is determined to be ineffective.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

+ Details

Name:	us-gaap_UnrealizedGainLossOnCashFlowHedgingInstruments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=mro_ThreeWayCollarsNaturalGasQ12020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=mro_ThreeWayCollarsNaturalGasQ12020CeilingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=mro_ThreeWayCollarsNaturalGasQ12020FloorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=mro_ThreeWayCollarsNaturalGasQ12020SoldPutMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivatives - Narrative (Details) $ in Millions	1 Months Ended	9 Months Ended	12 Months Ended
Derivatives - Narrative (Details) $ in Millions	Feb. 10, 2020 Bbls_per_day $ / bbl	Sep. 30, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax			$ 0	$ 0	$ 47
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax					$ 46
Interest Rate Swap [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cash Proceeds Received from Derivatives		$ 54
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount				$ 0
Unrealized Gain (Loss) on Cash Flow Hedging Instruments			(2)
Cash Flow Hedging [Member] \| Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount			$ 320
Subsequent Event [Member] \| Three-Way Collars - Natural Gas Q1 2020 [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Volume \| Bbls_per_day	20,000
Subsequent Event [Member] \| Three-Way Collars - Natural Gas Q1 2020, Ceiling [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Weighted average price \| $ / bbl	66.37
Subsequent Event [Member] \| Three-Way Collars - Natural Gas Q1 2020, Floor [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Weighted average price \| $ / bbl	55.00
Subsequent Event [Member] \| Three-Way Collars - Natural Gas Q1 2020, Sold Put [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Weighted average price \| $ / bbl	48.00