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Annual report pursuant to Section 13 and 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS (Impairment Charges on Financial and Nonfinancial Assets) (Details)

v3.3.1.900
FAIR VALUE OF FINANCIAL INSTRUMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS (Impairment Charges on Financial and Nonfinancial Assets) (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Goodwill, Impairment Loss Ìý $ 0.0 $ 73.5 Ìý
Tangible Asset Impairment Charges Ìý Ìý 537.8 Ìý
Impairment of Intangible Assets (Excluding Goodwill) Ìý Ìý 13.8 Ìý
Other Asset Impairment Charges Ìý Ìý 562.0 Ìý
Assets, Fair Value Disclosure, Nonrecurring $ 397.2 Ìý 79.4 Ìý
Impairment Charges 269.5 Ìý 644.7 Ìý
Fair Value, Inputs, Level 1 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring 0.0 Ìý 0.0 Ìý
Fair Value, Inputs, Level 2 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring 397.2 Ìý 0.0 Ìý
Fair Value, Inputs, Level 3 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring 0.0 Ìý 79.4 Ìý
Global Exploration Investment in Venture [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Equity Method Investment, Other than Temporary Impairment Ìý Ìý 9.2 Ìý
Global Exploration Investment in Venture [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Global Exploration Investment in Venture [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Global Exploration Investment in Venture [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Amapa [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Equity Method Investment, Other than Temporary Impairment Ìý Ìý Ìý $ 67.6
Asia Pacific Iron Ore [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Goodwill, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Goodwill, Impairment Loss Ìý Ìý 73.5 Ìý
Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Goodwill, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Goodwill, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Goodwill, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Other Reporting Units [Member] | Other Reporting Units [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Tangible Asset Impairment Charges Ìý Ìý 11.3 Ìý
Other Reporting Units [Member] | Other Reporting Units [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Other Reporting Units [Member] | Other Reporting Units [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Other Reporting Units [Member] | Other Reporting Units [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Asia Pacific [Member] | Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Finite-lived Intangible Assets, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Asia Pacific Iron Ore [Member] | Asia Pacific Iron Ore [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý Ìý 72.4 Ìý
Tangible Asset Impairment Charges Ìý Ìý 526.5 Ìý
Finite-lived Intangible Assets, Fair Value Disclosure Ìý Ìý 7.0 Ìý
Impairment of Intangible Assets (Excluding Goodwill) Ìý Ìý 24.2 Ìý
Asia Pacific Iron Ore [Member] | Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Finite-lived Intangible Assets, Fair Value Disclosure Ìý Ìý 0.0 Ìý
Asia Pacific Iron Ore [Member] | Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý Ìý 72.4 Ìý
Finite-lived Intangible Assets, Fair Value Disclosure Ìý Ìý 7.0 Ìý
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Debt Instrument, Fair Value Disclosure 397.2 Ìý Ìý Ìý
Gain on new debt issued 269.5 Ìý Ìý Ìý
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Debt Instrument, Fair Value Disclosure 0.0 Ìý Ìý Ìý
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Debt Instrument, Fair Value Disclosure 397.2 $ 134.7 $ 0.0 Ìý
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý Ìý Ìý
Debt Instrument, Fair Value Disclosure $ 0.0 Ìý Ìý Ìý