ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Environmental	$ 2.0	$ 2.5
Asset Retirement Obligation	165.3	172.4	$ 168.4
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent	167.3	174.9
Accrued Reclamation Costs, Current	2.4	2.9
Environmental and mine closure obligations	164.9	172.0
Mining and Pelletizing [Member] \| Operating Segments [Member]
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 22.0	$ 35.0

Environmental Loss Contingency And 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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Current portion of reclamation reserve to restore a mining or drilling site to the condition agreed upon within the mining or drilling contract.

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The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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