Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value Measurements, Nonrecurring) (Details)

v3.3.0.814
FAIR VALUE OF FINANCIAL INSTRUMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value Measurements, Nonrecurring) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Mar. 31, 2015
Sep. 30, 2015
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Goodwill, Impairment Loss   $ 0.0 $ 73.5
Assets, Fair Value Disclosure, Nonrecurring $ 397.2   79.4
Impairment of goodwill and other long-lived assets 269.5   644.7
Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Nonrecurring 0.0   0.0
Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Nonrecurring 397.2   0.0
Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets, Fair Value Disclosure, Nonrecurring 0.0   79.4
Global Exploration Investment in Venture [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity Method Investments, Fair Value Disclosure     0.0
Equity Method Investment, Other than Temporary Impairment     9.2
Global Exploration Investment in Venture [Member] | Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity Method Investments, Fair Value Disclosure     0.0
Global Exploration Investment in Venture [Member] | Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity Method Investments, Fair Value Disclosure     0.0
Global Exploration Investment in Venture [Member] | Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity Method Investments, Fair Value Disclosure     0.0
Asia Pacific Iron Ore [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Goodwill, Fair Value Disclosure     0.0
Goodwill, Impairment Loss     73.5
Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Goodwill, Fair Value Disclosure     0.0
Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Goodwill, Fair Value Disclosure     0.0
Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Goodwill, Fair Value Disclosure     0.0
Other Reporting Units [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure     0.0
Tangible Asset Impairment Charges     11.3
Other Reporting Units [Member] | Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure     0.0
Other Reporting Units [Member] | Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure     0.0
Other Reporting Units [Member] | Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure     0.0
Asia Pacific [Member] | Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure     0.0
Finite-lived Intangible Assets, Fair Value Disclosure     0.0
Asia Pacific Iron Ore [Member] | Asia Pacific Iron Ore [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure     72.4
Tangible Asset Impairment Charges     526.5
Other Asset Impairment Charges     24.2
Finite-lived Intangible Assets, Fair Value Disclosure     7.0
Asia Pacific Iron Ore [Member] | Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure     0.0
Finite-lived Intangible Assets, Fair Value Disclosure     0.0
Asia Pacific Iron Ore [Member] | Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure     72.4
Finite-lived Intangible Assets, Fair Value Disclosure     7.0
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Debt Instrument, Fair Value Disclosure 397.2    
Gain on new debt issued 269.5    
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Debt Instrument, Fair Value Disclosure 0.0    
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Debt Instrument, Fair Value Disclosure 397.2 $ 217.7 $ 0.0
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Debt Instrument, Fair Value Disclosure $ 0.0