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Dispositions (Oil and Gas Operations) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 10, 2017
Mar. 31, 2017
Mar. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Net gain on sales of assets   $ (23.0) $ 0.0
Freeport-McMoRan Oil & Gas | Elk Petroleum [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Net gain on sales of assets   $ (17.0)  
Proceeds from sales $ 17.5