ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Environmental	$ 2.4	$ 2.5
Asset Retirement Obligation	174.9	172.4	$ 168.4
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent	177.3	174.9
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current	2.9	2.9
Environmental Loss Contingency And Mine Reclamation And Closing Liability Noncurrent	174.4	172.0
Mining and Pelletizing [Member]
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 174.9	$ 172.4

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
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-Topic 410
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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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