Representing the right to extract oil or gas subject to such terms as may be imposed by the conveyance

Name:	mro_Concessions
Namespace Prefix:	mro
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Acreage is considered to be both developed and undeveloped. Developed acres are acres spaced or assigned to productive wells. Undeveloped acreage are those lease acres on which wells have not been drilled or completed to a point that would permit the producing.

+ Details

Name:	mro_GasAndOilAcreagesUndevelopedAndDevelopedNet
Namespace Prefix:	mro
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Working interest percentage for each asset.

+ Details

Name:	mro_WorkingInterestPercentage
Namespace Prefix:	mro
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The aggregate value (measured at the lower of net carrying value or fair value less cost of disposal) for assets of a disposal group, including a component of the entity (discontinued operation), to be sold or that has been disposed of through sale, as of the financial statement date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 144

-Paragraph 46

+ Details

Name:	us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 159

-Paragraph 18

-Subparagraph f

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 18

-Paragraph 20

-Subparagraph a (1)

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	instant

- 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.

+ Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from the sale of property, plant and equipment (capital expenditures), software, and other intangible assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 15

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 16

-Subparagraph c

+ Details

Name:	us-gaap_ProceedsFromSaleOfProductiveAssets
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The value of all consideration given or received by the Entity in the significant acquisition or disposal.

+ Details

Name:	us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The difference between the value of the consideration received by the Entity on the sale or disposal and net book value of assets sold or disposed, before any tax related impact.

+ Details

Name:	us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Dispositions (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended			9 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Jun. 30, 2011	Sep. 30, 2010 Angola [Member]	Sep. 30, 2011 Angola [Member] Held [Member]	Sep. 30, 2011 Angola [Member] Disposed [Member]	Sep. 30, 2011 Gudrun [Member]	Sep. 30, 2011 DJ Basin [Member]	Sep. 30, 2011 DJ Basin [Member] Disposed [Member]	Sep. 30, 2011 Alaska [Member]	Sep. 30, 2011 Poland Total [Member]	Sep. 30, 2011 Poland Total [Member] Held [Member]	Sep. 30, 2011 Poland April [Member] Held [Member]	Sep. 30, 2011 Poland April [Member] Disposed [Member]	Sep. 30, 2011 Poland July [Member] Disposed [Member]	Dec. 31, 2011 GOM Pipelines [Member]	Dec. 31, 2011 Poseidon [Member]	Dec. 31, 2011 Odyssey [Member]	Dec. 31, 2011 Eugene Island [Member]
Dispositions Detail [Line Items]
Proceeds from disposal of assets	$ 385	$ 1,354		$ 1,300			$ 85	$ 270
Pretax gain (loss) on sale				811			(64)	37		8	12
Transaction value																206
Total assets held for sale			$ 23,968													$ 45
Working interest percentage					10.00%	20.00%			30.00%			51.00%		40.00%	9.00%
Gas and oil acreages, net								180,000
Concessions													10
Ownership Percentage																	28.00%	29.00%	23.00%