Change in Basic EPS for Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition

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Change in Diluted EPS for Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition

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Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition

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Loss on sale of Cliffs Logan County Coal

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Proceeds from sale of Cliffs Logan County Coal

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Sale Price of CLCC Assets

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of income (loss) from continuing operations attributable to the parent. Also defined as revenue less expenses and taxes from ongoing operations before extraordinary items but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) QUARTERLY RESULTS OF OPERATIONS (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income (Loss) from Continuing Operations Attributable to Parent	$ (1,285,100,000)	$ (5,879,600,000)	$ 10,900,000	$ (70,300,000)	$ 43,300,000	$ 115,200,000	$ 146,000,000	$ 107,000,000	$ (7,224,200,000)	$ 411,500,000	$ (935,300,000)
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	25.2							12.9	25.2
Goodwill, Impairment Loss									73,500,000us-gaap_GoodwillImpairmentLoss	80,900,000us-gaap_GoodwillImpairmentLoss
Loss on sale of Cliffs Logan County Coal									419,600,000clf_LossonsaleofCliffsLoganCountyCoal	0clf_LossonsaleofCliffsLoganCountyCoal	0clf_LossonsaleofCliffsLoganCountyCoal
Sale Price of CLCC Assets									174,000,000clf_SalePriceofCLCCAssets
Proceeds from sale of Cliffs Logan County Coal									155,000,000	0	0
Income Tax Expense (Benefit)	(289,700,000)us-gaap_IncomeTaxExpenseBenefit								(1,302,000,000)us-gaap_IncomeTaxExpenseBenefit	55,100,000us-gaap_IncomeTaxExpenseBenefit	255,900,000us-gaap_IncomeTaxExpenseBenefit
Asset Impairment Charges									9,029,900,000.0us-gaap_AssetImpairmentCharges	250,800,000.0us-gaap_AssetImpairmentCharges	1,049,900,000.0us-gaap_AssetImpairmentCharges
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
Goodwill, Impairment Loss										80,900,000
Wabush [Member]
Asset Impairment Charges									154,600,000.0
Bloom Lake [Member]
Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition										45,100,000
Change in Basic EPS for Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition					$ 0.29					$ 0.30	$ 0	$ 0.07
Change in Diluted EPS for Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition										$ 0.26	$ 0.25	$ 0.07
Minimum [Member]
Income (Loss) from Continuing Operations Attributable to Parent									300,000
Maximum [Member]
Income (Loss) from Continuing Operations Attributable to Parent									800,000
Bloom Lake [Member]
Asset Impairment Charges									$ 1,300,000,000.0