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Dispositions - International E&P Segment (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Mar. 01, 2018	Jun. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of oil and gas property and equipment				$ 1,183	$ 1,726
International Exploration and Production [Member] \| Non-Core Property, Second Quarter 2018 Agreement [Member] \| Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of oil and gas property and equipment		$ 56
Disposal group, assets		77		77
Disposal group, liabilities		11		11
International Exploration and Production [Member] \| Marathon Oil Libya Limited [Member] \| Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of oil and gas property and equipment	$ 450
Net gain (loss) on disposal of assets	$ 255
Ownership percentage by parent	16.33%
International Exploration and Production [Member] \| Non-Core Property, Third Quarter 2017 Agreement [Member] \| Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of oil and gas property and equipment			$ 53
Disposal group, assets		62		62
Disposal group, liabilities		$ 4		$ 4