Business exit costs (Details 4) - Other restructuring [Member] - Discontinued operations, held-for-sale or disposed of by sale - USD ($)	3 Months Ended	33 Months Ended
	Mar. 31, 2018	Mar. 31, 2018
Refining
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs	$ 0
Exploration and production
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs	$ 0	$ 10,500,000