Cleveland-Cliffs Inc. Annual report pursuant to Section 13 and 15(d)

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)

FAIR VALUE OF FINANCIAL INSTRUMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS (Impairment Charges on Financial and Nonfinancial Assets) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Impairment Loss	$ 73.5us-gaap_GoodwillImpairmentLoss	$ 80.9us-gaap_GoodwillImpairmentLoss
Tangible Asset Impairment Charges	8,839.0us-gaap_TangibleAssetImpairmentCharges
Finite-lived Intangible Assets, Fair Value Disclosure		1.6
Impairment of Intangible Assets (Excluding Goodwill)	15.5	14.5
Other Asset Impairment Charges	8,956.4us-gaap_OtherAssetImpairmentCharges
Equity Method Investment, Other than Temporary Impairment	0	0	(365.4)
Assets, Fair Value Disclosure, Nonrecurring	438.9	47.9
Impairment Charges	9,039.1clf_ImpairmentCharges	318.4clf_ImpairmentCharges
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
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finite-lived Intangible Assets, Fair Value Disclosure		1.6
Assets, Fair Value Disclosure, Nonrecurring	438.9	47.9
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
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
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
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
Amapa [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure		0
Equity Method Investment, Other than Temporary Impairment		67.6	(365.4)
Amapa [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
Amapa [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
Amapa [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
Asia Pacific Iron Ore [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure	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
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
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
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure		0
Goodwill, Impairment Loss		80.9
Cliffs Chromite Ontario and Cliffs Chromite Far North [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
Cliffs Chromite Ontario and Cliffs Chromite Far North [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
Cliffs Chromite Ontario and Cliffs Chromite Far North [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
Wabush [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible Asset Impairment Charges		145.1
Impairment of Long-Lived Assets Held-for-use	140.1	49.9
Impairment of Intangible Assets (Excluding Goodwill)		9.5
Wabush [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finite-lived Intangible Assets, Fair Value Disclosure		0
Wabush [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finite-lived Intangible Assets, Fair Value Disclosure		0
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure		46.3
Tangible Asset Impairment Charges		155.4
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [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
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [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
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [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		46.3
CQIM Reporting Unit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Impairment Loss		997.3
Other Reporting Units [Member] \| 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
Tangible Asset Impairment Charges	19.2
Other Reporting Units [Member] \| 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
Other Reporting Units [Member] \| 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
Other Reporting Units [Member] \| 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
Bloom Lake [Member] \| Eastern Canadian Iron Ore [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	187.9
Tangible Asset Impairment Charges	7,043.7
Finite-lived Intangible Assets, Fair Value Disclosure	0
Impairment of Intangible Assets (Excluding Goodwill)	56.2
Bloom Lake [Member] \| Eastern Canadian 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
Finite-lived Intangible Assets, Fair Value Disclosure	0
Bloom Lake [Member] \| Eastern Canadian 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
Finite-lived Intangible Assets, Fair Value Disclosure	0
Bloom Lake [Member] \| Eastern Canadian 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	187.9
Finite-lived Intangible Assets, Fair Value Disclosure	0
CLCC [Member] \| North American Coal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	62.6
Tangible Asset Impairment Charges	195.5
CLCC [Member] \| North American Coal [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
CLCC [Member] \| North American Coal [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
CLCC [Member] \| North American Coal [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	62.6
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
Finite-lived Intangible Assets, Fair Value Disclosure	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
Finite-lived Intangible Assets, Fair Value Disclosure	7.0
Impairment of Intangible Assets (Excluding Goodwill)	24.2
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
Finite-lived Intangible Assets, Fair Value Disclosure	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
Ferroalloys [Member] \| Ferroalloys [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	12.2
Tangible Asset Impairment Charges	259.5
Finite-lived Intangible Assets, Fair Value Disclosure	0
Impairment of Intangible Assets (Excluding Goodwill)	0.3
Ferroalloys [Member] \| Ferroalloys [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
Finite-lived Intangible Assets, Fair Value Disclosure	0
Ferroalloys [Member] \| Ferroalloys [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
Finite-lived Intangible Assets, Fair Value Disclosure	0
Ferroalloys [Member] \| Ferroalloys [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	12.2
Finite-lived Intangible Assets, Fair Value Disclosure	0
Wabush [Member] \| Eastern Canadian Iron Ore [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	42.7
Tangible Asset Impairment Charges	132.6
Finite-lived Intangible Assets, Fair Value Disclosure	0
Impairment of Intangible Assets (Excluding Goodwill)	36.7
Wabush [Member] \| Eastern Canadian 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
Finite-lived Intangible Assets, Fair Value Disclosure	0
Wabush [Member] \| Eastern Canadian 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
Finite-lived Intangible Assets, Fair Value Disclosure	0
Wabush [Member] \| Eastern Canadian 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	42.7
Finite-lived Intangible Assets, Fair Value Disclosure	0
Oak Grove [Member] \| North American Coal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	23.4
Tangible Asset Impairment Charges	267.5
Oak Grove [Member] \| North American Coal [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
Oak Grove [Member] \| North American Coal [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
Oak Grove [Member] \| North American Coal [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	23.4
Pinnacle [Member] \| North American Coal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant, and Equipment, Fair Value Disclosure	30.7
Tangible Asset Impairment Charges	394.5
Pinnacle [Member] \| North American Coal [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
Pinnacle [Member] \| North American Coal [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
Pinnacle [Member] \| North American Coal [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	$ 30.7