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Quarterly report pursuant to Section 13 or 15(d)

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

v2.4.0.8
FAIR VALUE OF FINANCIAL INSTRUMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS (Impairment Charges on Financial and Nonfinancial Assets) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2014
Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Impairment Loss $ 0 $ 80.9
ASSETS: Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring Ìý 47.9
Impairment Charges Ìý 318.4
Fair Value, Inputs, Level 1 [Member]
 Ìý Ìý
ASSETS: Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring Ìý 0
Fair Value, Inputs, Level 2 [Member]
 Ìý Ìý
ASSETS: Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring Ìý 0
Fair Value, Inputs, Level 3 [Member]
 Ìý Ìý
ASSETS: Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring Ìý 47.9
Amapa [Member]
 Ìý Ìý
ASSETS: Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý 0
Equity Method Investment, Other than Temporary Impairment Ìý 67.6
Amapa [Member] | Fair Value, Inputs, Level 1 [Member]
 Ìý Ìý
ASSETS: Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý 0
Amapa [Member] | Fair Value, Inputs, Level 2 [Member]
 Ìý Ìý
ASSETS: Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý 0
Amapa [Member] | Fair Value, Inputs, Level 3 [Member]
 Ìý Ìý
ASSETS: Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý 0
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Fair Value Disclosure Ìý 0
Goodwill, Impairment Loss Ìý 80.9
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Fair Value, Inputs, Level 1 [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Fair Value Disclosure Ìý 0
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Fair Value, Inputs, Level 2 [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Fair Value Disclosure Ìý 0
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Fair Value, Inputs, Level 3 [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Fair Value Disclosure Ìý 0
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 46.3
Impairment of Long-Lived Assets Held-for-use Ìý 155.4
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Fair Value, Inputs, Level 1 [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 0
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Fair Value, Inputs, Level 2 [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 0
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Fair Value, Inputs, Level 3 [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 46.3
Wabush [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Finite-lived Intangible Assets, Fair Value Disclosure Ìý 1.6
Other Asset Impairment Charges Ìý 14.5
Wabush [Member] | Fair Value, Inputs, Level 1 [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Finite-lived Intangible Assets, Fair Value Disclosure Ìý 0
Wabush [Member] | Fair Value, Inputs, Level 2 [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Finite-lived Intangible Assets, Fair Value Disclosure Ìý 0
Wabush [Member] | Fair Value, Inputs, Level 3 [Member]
 Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Finite-lived Intangible Assets, Fair Value Disclosure Ìý $ 1.6