Dispositions Income (loss) from discontinued operations (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments	$ 0		$ 0	$ 4	$ 1
Oil Sands Mining Segment [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue	173		199	431	359
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	(43)		0	(43)	0
DIsposal group, Not Discontinued Operation, Total Revenues and Other Income	130		199	388	359
Disposal Group, Including Discontinued Operation, Production Expense	103		165	254	306
Disposal Group, Including Discontinued Operation, Depreciation and Amortization	1		49	40	109
Impairments	0	$ 6,600	0	6,636	0
Disposal Group, Including Discontinued Operation, Other Expense	12		31	25	60
Disposal Group, Including Discontinued Operation, Operating Expense	116		245	6,955	475
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	14		(46)	(6,567)	(116)
Discontinued Operation, Tax (Expense) Benefit from Provision for (Gain) Loss on Disposal	0		(14)	(1,674)	(37)
Discontinued Operation, Provision for Loss (Gain) on Disposal, Net of Tax	$ 14		$ (32)	$ (4,893)	$ (79)