Dispositions Discontinued Operations, Balance Sheet Disclosures (Details) - USD ($) $ in Millions	2 Months Ended	3 Months Ended			9 Months Ended
	Apr. 30, 2016	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Current assets held for sale		$ 11			$ 11		$ 227
Assets Held-for-sale, Not Part of Disposal Group, Current		11			11		1
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent		54			54		9,098
Disposal Group, Including Discontinued Operation, Liabilities, Current		0			0		121
Current Liabilities Held for Sale, Continuing Operations		0			0		0
Proceeds from Sale of Oil and Gas Property and Equipment					1,757	$ 837
Oil Sands Mining Segment [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal		0		$ 0	(43)	$ 0
Oil Sands Mining Segment [Member] | Discontinued Operations, Held-for-sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents		0			0		2
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net		0			0		129
Disposal Group, Including Discontinued Operation, Inventory, Current		0			0		91
Disposal Group, Including Discontinued Operation, Other Assets, Current		0			0		4
Current assets held for sale		0			0		226
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment, Noncurrent		0			0		8,991
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent		0			0		106
Disposal Group, Including Discontinued Operation, Assets		0			0		9,097
Assets Held-for-sale, Not Part of Disposal Group, Current		54			54		1
Assets of disposal group classified as held for sale		54			54		9,098
Disposal Group, Including Discontinued Operation, Accounts Payable, Current		0			0		111
Disposal Group, Including Discontinued Operation, Accrued Liabilities, Current		0			0		10
Disposal Group, Including Discontinued Operation, Liabilities, Current		0			0		121
Disposal Group, Including Discontinued Operation, Pension Plan Benefit Obligation, Noncurrent		0			0		95
Disposal Group, Including Discontinued Operation, Deferred Tax Liabilities		0			0		1,669
Disposal Group, Including Discontinued Operation, Other Liabilities		0			0		20
Disposal Group, Including Discontinued Operation, Liabilities		0			0		1,784
Liabilities of Disposal Group in Continuing Operations		9			9		7
Liabilities of disposal group associated with assets held for sale		$ 9			$ 9		$ 1,791
Shenandoah in Gulf of Mexico, Piceance in Colorado, and West Texas [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]
Disposal Group, Including Discontinued Operation, Working Capital Interest To Be Disposed Of	10.00%
Proceeds from Sale of Oil and Gas Property and Equipment	$ 80
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal			$ (48)