Annual report pursuant to Section 13 and 15(d)

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details)

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ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Loss Contingencies [Line Items]      
Environmental $ 2.5 $ 2.9  
Asset Retirement Obligation 172.4 168.4 $ 187.8
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent 174.9 171.3  
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current 2.9 3.6  
Environmental Loss Contingency And Mine Reclamation And Closing Liability Noncurrent 172.0 167.7  
Mining and Pelletizing [Member]      
Loss Contingencies [Line Items]      
Asset Retirement Obligation $ 172.4 $ 168.4