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ASSET RETIREMENT OBLIGATIONS (Summary Of Asset Retirement Obligations) (Details) - USD ($) $ in Millions | Mar. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
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Loss Contingencies [Line Items] |  |  |  |  |
Asset Retirement Obligation | $ 181.4 | [1] | $ 165.3 | [1] | $ 172.4
Asset Retirement Obligation, Current | 2.2 |  | 2.1 |  |
Asset Retirement Obligations, Noncurrent | 179.2 |  | 163.2 |  |
Operating Segments [Member] | Mining and Pelletizing [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Asset Retirement Obligation | $ 32.5 |  | $ 22.0 |  |
[1] | 1 Includes $32.5 million and $22.0 million related to our active operations as of March 31, 2020 and December 31, 2019, respectively.

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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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