Derivatives (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Interest rate [Member] \| Fair Value Hedges [Member] \| Other Noncurrent Assets [Member] \| Net Asset [Member]
Derivatives at Fair Value on Balance Sheet [Line Items]
Derivative asset designated as hedging instrument fair value	$ 28	$ 32
Derivative net asset designated as hedging instrument fair value	28	32
Commodity [Member] \| Not Designated as Hedges [Member] \| Other Current Liabilities [Member] \| Net Liability [Member]
Derivatives at Fair Value on Balance Sheet [Line Items]
Derivative asset not designated as hedging instrument fair value		1
Derivative liability not designated as hedging instrument fair value		3
Derivative net liability not designated as hedging instrument fair value		2
Commodity [Member] \| Other Current Assets [Member] \| Net Asset [Member]
Derivatives at Fair Value on Balance Sheet [Line Items]
Derivative asset not designated as hedging instrument fair value	1	58
Derivative liability not designated as hedging instrument fair value		102
Derivative net asset not designated as hedging instrument fair value	1	(44)
Not Designated as Hedges [Member] \| Net Liability [Member]
Derivatives at Fair Value on Balance Sheet [Line Items]
Derivative asset not designated as hedging instrument fair value		1
Derivative liability not designated as hedging instrument fair value		3
Derivative net liability not designated as hedging instrument fair value		2
Net Asset [Member]
Derivatives at Fair Value on Balance Sheet [Line Items]
Derivative asset designated as hedging instrument fair value	28	32
Derivative asset not designated as hedging instrument fair value	1	58
Derivative fair value of derivative asset	29	90
Derivative liability not designated as hedging instrument fair value		102
Derivative fair value of derivative liability		102
Derivative net asset designated as hedging instrument fair value	28	32
Derivative net asset not designated as hedging instrument fair value	1	(44)
Fair value of derivative net asset	29	(12)
Net Liability [Member]
Derivatives at Fair Value on Balance Sheet [Line Items]
Derivative fair value of derivative asset		1
Derivative fair value of derivative liability		3
Fair value of derivative net liability		$ 2

Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position. These are fair values whose balances are recorded as a net asset in the statement of financial position.

Name:	mro_DerivativeFairValueOfDerivativeNetAsset
Namespace Prefix:	mro
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position. These are fair values whose balances are recorded as a net liability in the statement of financial position.

+ Details

Name:	mro_DerivativeFairValueOfDerivativeNetLiability
Namespace Prefix:	mro
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of a derivative asset (or nonderivative instrument) that is designated and qualifies as a hedging instrument, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position. These are fair values whose balances are recorded as a net asset in the statement of financial position.

+ Details

Name:	mro_DerivativeNetAssetDesignatedAsHedgingInstrumentFairValue
Namespace Prefix:	mro
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of a derivative asset that is not designated or qualifying as a hedging instrument, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position

+ Details

Name:	mro_DerivativeNetAssetNotDesignatedAsHedgingInstrumentFairValue
Namespace Prefix:	mro
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of a derivative liability that is not designated or qualifying as a hedging instrument, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ Details

Name:	mro_DerivativeNetLiabilityNotDesignatedAsHedgingInstrumentFairValue
Namespace Prefix:	mro
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44C

-Subparagraph a

-Clause 1

+ Details

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

- Definition

+ References

+ Details

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

- Definition

+ References

+ Details

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

- Definition

+ References

+ Details

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

- Definition

+ References

+ Details

Name:	us-gaap_DerivativeLiabilityNotDesignatedAsHedgingInstrumentFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration