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Impairment fair value, ceiling test and transactions costs (Details 5) - USD ($)	3 Months Ended
	Jun. 30, 2016	Mar. 31, 2016
Exploration and production [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair value impairment	$ 900,000	$ (1,400,000)
Fair value impairment after tax	600,000	$ (900,000)
Refining [Member] | Discontinued operations, held-for-sale or disposed by sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair value impairment	251,900,000
Fair value impairment after tax	$ 156,700,000

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- Definition

Amount before tax of (gain) loss recognized for the (reversal of write-down) write-down to fair value, less cost to sell, of a discontinued operation.

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