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FAIR VALUE MEASUREMENTS (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | Dec. 31, 2016
Fair Value, Assets And Liabilities Components [Line Items] |  |  |  |  |
Loans Receivable, Fair Value Disclosure | $ 7.7 |  | $ 7.7 |  |
Contingent Liabilities recognized in Consolidated Financials | 0.0 |  | 0.0 |  | $ 37.2
Cash equivalents | 77.0 |  | $ 77.0 |  | 177.0
Management Estimate of 62% Fe |  |  | 62.00% |  |
Derivative Asset | 89.5 |  | $ 89.5 |  | 33.1
Derivative Asset, Current | 89.5 |  | 89.5 |  | 33.1
Derivative Liability, Current | 9.3 |  | 9.3 |  | 0.5
Derivative Liability | 9.3 |  | 9.3 |  | 0.5
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, NET OF TAX | 32.3 | $ (2.7) | (13.6) | $ (0.6) |
Fair Value, Inputs, Level 1 [Member] |  |  |  |  |
Fair Value, Assets And Liabilities Components [Line Items] |  |  |  |  |
Cash equivalents | 40.0 |  | 40.0 |  | 177.0
Derivative Asset | 0.0 |  | 0.0 |  | 0.0
Derivative Liability | 0.0 |  | 0.0 |  | 0.0
Fair Value, Inputs, Level 2 [Member] |  |  |  |  |
Fair Value, Assets And Liabilities Components [Line Items] |  |  |  |  |
Cash equivalents | 37.0 |  | 37.0 |  | 0.0
Derivative Asset | 0.0 |  | 0.0 |  | 1.5
Derivative Liability | 0.0 |  | 0.0 |  | 0.0
Fair Value, Inputs, Level 3 [Member] |  |  |  |  |
Fair Value, Assets And Liabilities Components [Line Items] |  |  |  |  |
Contingent Liabilities recognized in Consolidated Financials | 0.0 |  | 0.0 |  |
Cash equivalents | 0.0 |  | 0.0 |  | 0.0
Derivative Asset | 89.5 |  | 89.5 |  | 31.6
Derivative Liability | 9.3 |  | 9.3 |  | 0.5
Not Designated as Hedging Instrument [Member] |  |  |  |  |
Fair Value, Assets And Liabilities Components [Line Items] |  |  |  |  |
Derivative Asset | 89.5 |  | 89.5 |  | 33.1
Derivative Liability | 9.3 |  | 9.3 |  | 0.5
Derivative Financial Instruments, Assets [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] |  |  |  |  |
Fair Value, Assets And Liabilities Components [Line Items] |  |  |  |  |
Derivative Asset, Current | 84.8 |  | 84.8 |  | 21.3
U S Iron Ore And Asia Pacific Iron Ore [Member] | Derivative Financial Instruments, Assets [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] |  |  |  |  |
Fair Value, Assets And Liabilities Components [Line Items] |  |  |  |  |
Derivative Asset, Current | $ 4.7 |  | $ 4.7 |  | $ 10.3

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