Dispositions Income (loss) from discontinued operations (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments	$ 201		$ 47	$ 205	$ 48
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	0		239	431	598
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	0		0	(43)	0
DIsposal group, Not Discontinued Operation, Total Revenues and Other Income	0		239	388	598
Disposal Group, Including Discontinued Operation, Production Expense	0		135	254	441
Disposal Group, Including Discontinued Operation, Depreciation and Amortization	0		72	40	181
Impairments	0	$ 6,600	0	6,636	0
Disposal Group, Including Discontinued Operation, Other Expense	0		9	25	69
Disposal Group, Including Discontinued Operation, Operating Expense	0		216	6,955	691
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	0		23	(6,567)	(93)
Discontinued Operation, Tax (Expense) Benefit from Provision for (Gain) Loss on Disposal	0		9	(1,674)	(28)
Discontinued Operation, Provision for Loss (Gain) on Disposal, Net of Tax	$ 0		$ 14	$ (4,893)	$ (65)