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Impairment fair value and ceiling test (Details 3) - Discontinued operations, held-for-sale or disposed of by sale [Member] - USD ($)	3 Months Ended				9 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2015
Refining [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
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)	$ 356,100,000		$ 756,100,000
Fair value impairment after tax	$ 600,000	$ (900,000)	$ 224,400,000		$ 476,400,000
Impairment of oil and gas properties				$ 500,400,000
Impairment of oil and gas properties, after tax				$ 315,300,000

X

- Definition

The after tax expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced.

+ References

No definition available.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1
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- Definition

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

+ References

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- Definition

The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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