Inventories (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Inventory Disclosure [Abstract]
Liquid hydrocarbons, natural gas and bitumen	$ 58	$ 55
Supplies and sundry items	299mro_InventorySuppliesAndSundry	309mro_InventorySuppliesAndSundry
Inventories at cost	357us-gaap_InventoryNet	364us-gaap_InventoryNet
Percentage of LIFO Inventory	6.00%us-gaap_PercentageOfLIFOInventory	4.00%us-gaap_PercentageOfLIFOInventory
Excess of Replacement or Current Costs over Stated LIFO Value	$ 20	$ 32

Carrying amount as of the balance sheet date of sundry items and miscellaneous supplies.

No definition available.

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- Definition

Carrying amount as of the balance sheet date of crude oil, natural gas liquids, natural gas and bitumen inventories.

+ References

No definition available.

+ Details

Name:	mro_LiquidHydrocarbonsNaturalGasAndBitumen
Namespace Prefix:	mro_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The excess of replacement or current cost over the stated LIFO (last in first out) inventory value when the LIFO inventory method is utilized.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Details

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- Definition

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 330

-SubTopic 10

-Section 35

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6386567&loc=d3e3927-108312

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section 45

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The percentage of LIFO (last in first out) inventory to total inventory as of the balance sheet date if other than 100 percent.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	instant