Leases - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Weighted average lease term	3 years
Discount rate	4.00%
Annual payments to be received	$ 6
Maximum financing available		$ 380
Total costs incurred under lease	$ 54
Term of contract	5 years
Finance lease extension term	5 years
Residual value guarantee		89.00%

Lessee, Finance Lease, Maximum Financing Available

No definition available.

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Namespace Prefix:	mro_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Lessee, Finance Lease, Residual Value Guarantee, Percentage

+ References

No definition available.

+ Details

Name:	mro_LesseeFinanceLeaseResidualValueGuaranteePercentage
Namespace Prefix:	mro_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Lessee, Finance Lease, Total Costs Incurred

+ References

No definition available.

+ Details

Name:	mro_LesseeFinanceLeaseTotalCostsIncurred
Namespace Prefix:	mro_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Lessor, Operating Lease, Annual Payments to be Received

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Term of lessee's finance lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeFinanceLeaseRenewalTerm1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Term of lessee's finance lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_LesseeFinanceLeaseTermOfContract1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Discount rate used by lessee to determine present value of operating lease payments.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 55
-Paragraph 53
-URI http://asc.fasb.org/extlink&oid=77888399&loc=SL77918982-209971

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (g)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918686-209980

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant