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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2020 | Mar. 31, 2019
Schedule of Equity Method Investments [Line Items] |  |
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net | $ 32.8 |
Land Improvements [Member] | Minimum |  |
Schedule of Equity Method Investments [Line Items] |  |
Property, Plant and Equipment, Useful Life | 20 years |
Land Improvements [Member] | Maximum [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Property, Plant and Equipment, Useful Life | 45 years |
Buildings [Member] | Minimum |  |
Schedule of Equity Method Investments [Line Items] |  |
Property, Plant and Equipment, Useful Life | 40 years |
Buildings [Member] | Maximum [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Property, Plant and Equipment, Useful Life | 45 years |
Mining and Pelletizing Equipment [Member] | Minimum |  |
Schedule of Equity Method Investments [Line Items] |  |
Property, Plant and Equipment, Useful Life | 3 years |
Mining and Pelletizing Equipment [Member] | Maximum [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Property, Plant and Equipment, Useful Life | 20 years |
Steel and Manufacturing Equipment [Member] | Minimum |  |
Schedule of Equity Method Investments [Line Items] |  |
Property, Plant and Equipment, Useful Life | 3 years |
Steel and Manufacturing Equipment [Member] | Maximum [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Property, Plant and Equipment, Useful Life | 20 years |
Sales [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net | $ 26.8 | $ (5.5)

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