ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Environmental	$ 3.7	$ 5.5
Mine Reclamation and Closing Liability, current and noncurrent	165.3	165.3
Total environmental and mine closure obligations	169.0	170.8
Less current portion	3.4	5.2
Long term environmental and mine closure obligations	165.6	165.6
U.S. Iron Ore [Member] | Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	121.8	120.9
Asia Pacific Iron Ore [Member] | Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	20.3	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	$ 23.2	$ 22.9