Assets held for sale and discontinued operations Accounting pronouncement reclassification (Details 5) - Restatement adjustment [Member] - Accounting Standards Update 2015-17 [Member] - Exploration and production [Member] - Discontinued operations, held-for-sale or disposed of by sale [Member] $ in Millions	Sep. 30, 2016 USD ($)
Other current assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reclass to deferred tax asset	$ 47.5
Other current liabilities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Reclass to deferred tax asset	$ (4.1)