ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Environmental	$ 4.2	$ 5.5
Mine Reclamation and Closing Liability, current and noncurrent	214.0	165.3
Total environmental and mine closure obligations	218.2	170.8
Less current portion	3.3	5.2
Long term environmental and mine closure obligations	214.9	165.6
U.S. Iron Ore [Member] | Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	169.6	120.9
Asia Pacific Iron Ore [Member] | Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	20.8	21.5
LTV Steel Mining Company [Member] | Previously Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	$ 23.6	$ 22.9