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