Quarterly report pursuant to Section 13 or 15(d)

DISCONTINUED OPERATIONS (Schedule of Disposal Groups, including Discontinued Operations, Assets and Liabilities) (Details)

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DISCONTINUED OPERATIONS (Schedule of Disposal Groups, including Discontinued Operations, Assets and Liabilities) (Details) - USD ($)
$ in Millions
Sep. 30, 2018
Jan. 01, 2018
Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Current assets of discontinued operations $ 16.1 $ 118.5 $ 118.5
Current liabilities of discontinued operations 14.2 $ 75.0 75.0
Asia Pacific Iron Ore [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Cash and cash equivalents 15.6   29.4
Accounts receivable, net 0.0   33.9
Inventories 0.0   45.0
Supplies and other inventories 0.0   5.1
Other current assets 0.5   5.1
Current assets of discontinued operations 16.1   118.5
Property, plant and equipment, net 0.0   17.2
Other non-current assets 0.0   3.1
Total assets of discontinued operations 16.1   138.8
Accounts payable 4.2   28.2
Accrued liabilities 3.0   28.0
Other current liabilities 0.0   15.6
Current liabilities of discontinued operations 7.2   71.8
Environmental and mine closure obligations 0.0   28.8
Other liabilities 9.3   23.4
Total liabilities of discontinued operations $ 16.5   $ 124.0