ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Loss Contingencies [Line Items]
Environmental	$ 15.4	$ 15.7
Mine Reclamation and Closing Liability, current and noncurrent	237.0	249.4
Total environmental and mine closure obligations	252.4	265.1
Less current portion	12.0	12.3
Long term environmental and mine closure obligations	240.4	252.8
Previously Owned Or Operating Facilities [Member] \| LTV Steel Mining Company [Member]
Loss Contingencies [Line Items]
Mine closure	18.7	18.3
Owned Or Operating Facilities [Member] \| U.S. Iron Ore [Member]
Loss Contingencies [Line Items]
Mine closure	83.1	81.2
Owned Or Operating Facilities [Member] \| Eastern Canadian Iron Ore [Member]
Loss Contingencies [Line Items]
Mine closure	73.4	88.9
Owned Or Operating Facilities [Member] \| Asia Pacific Iron Ore [Member]
Loss Contingencies [Line Items]
Mine closure	22.7	22.4
Owned Or Operating Facilities [Member] \| North American Coal [Member]
Loss Contingencies [Line Items]
Mine closure	$ 39.1	$ 38.6

Environmental Loss Contingency And Mine Reclamation And Closing Liability Current

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Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent

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Amount of environmental loss contingencies, such as presence of hazardous waste, relevant information from reports issued by regulators, and estimated costs to achieve compliance with regulatory requirements. As well as, the amount of a reclamation and mine closing liability that is associated with a legal obligation for the closure and reclamation of a mine including the removal of buildings, equipment, machinery and other physical remnants of mining, closure of tailings impoundments, leach pads and other mine features, and contouring, covering and revegetation of waste rock piles and other disturbed areas.

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Mine Reclamation and Closing Liability, current and noncurrent

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Amount of a reclamation and mine closing liability that is associated with a legal obligation for the closure and reclamation of a mine including the removal of buildings, equipment, machinery and other physical remnants of mining, closure of tailings impoundments, leach pads and other mine features, and contouring, covering and revegetation of waste rock piles and other disturbed areas.

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