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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details)
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12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | 3 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2013
USD ($)
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Dec. 31, 2012
USD ($)
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Dec. 31, 2011
USD ($)
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Dec. 31, 2013
Amapa [Member]
USD ($)
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Dec. 31, 2012
Amapa [Member]
USD ($)
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Dec. 31, 2012
Renewafuel [Member]
USD ($)
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Dec. 31, 2011
Renewafuel [Member]
USD ($)
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Dec. 31, 2013
U.S. Iron Ore [Member]
USD ($)
Facility
T
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Dec. 31, 2012
U.S. Iron Ore [Member]
USD ($)
T
|
Dec. 31, 2011
U.S. Iron Ore [Member]
USD ($)
|
Dec. 31, 2013
Asia Pacific Iron Ore [Member]
USD ($)
Facility
|
Dec. 31, 2012
Asia Pacific Iron Ore [Member]
USD ($)
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Dec. 31, 2011
Asia Pacific Iron Ore [Member]
USD ($)
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Dec. 31, 2013
Asia Pacific Iron Ore [Member]
Cockatoo [Member]
USD ($)
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Dec. 31, 2012
Asia Pacific Iron Ore [Member]
Cockatoo [Member]
AUD
|
Dec. 31, 2012
Other Segment [Member]
USD ($)
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Dec. 31, 2013
Other Segment [Member]
USD ($)
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Dec. 31, 2011
Other Segment [Member]
USD ($)
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Dec. 31, 2013
North American Coal [Member]
USD ($)
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Dec. 31, 2012
North American Coal [Member]
USD ($)
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Dec. 31, 2011
North American Coal [Member]
USD ($)
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Dec. 31, 2013
Eastern Canadian Iron Ore [Member]
USD ($)
Facility
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Dec. 31, 2012
Eastern Canadian Iron Ore [Member]
USD ($)
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Dec. 31, 2011
Eastern Canadian Iron Ore [Member]
USD ($)
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Dec. 31, 2012
CQIM Reporting Unit [Member]
USD ($)
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Dec. 31, 2013
Wabush [Member]
USD ($)
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Dec. 31, 2012
Wabush [Member]
USD ($)
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Dec. 31, 2012
Sonoma [Member]
Asia Pacific Coal [Member]
AUD
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Jul. 10, 2012
Sonoma [Member]
Asia Pacific Coal [Member]
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Dec. 31, 2013
Empire [Member]
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Dec. 31, 2013
Black Label And Black Thor Chromite Deposits [Member]
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Dec. 31, 2013
Big Daddy Chromite Deposit [Member]
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Dec. 31, 2013
CLCC [Member]
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Dec. 31, 2013
Wabush [Member]
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Dec. 31, 2013
Bloom Lake [Member]
USD ($)
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Dec. 31, 2012
Bloom Lake [Member]
USD ($)
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Sep. 30, 2012
Bloom Lake [Member]
USD ($)
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Jun. 30, 2012
Bloom Lake [Member]
USD ($)
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Mar. 31, 2012
Bloom Lake [Member]
USD ($)
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Dec. 31, 2013
Bloom Lake [Member]
USD ($)
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Dec. 31, 2012
Bloom Lake [Member]
USD ($)
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Dec. 31, 2011
Bloom Lake [Member]
USD ($)
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Dec. 31, 2013
Investments in Ventures [Member]
Amapa [Member]
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Dec. 31, 2012
Investments in Ventures [Member]
Amapa [Member]
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Dec. 31, 2013
Metallurgical Coal Mines [Member]
North American Coal [Member]
Facility
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Dec. 31, 2013
Thermal Coal Mines [Member]
North American Coal [Member]
Facility
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Dec. 31, 2013
Take or Pay Contracts [Member]
USD ($)
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Dec. 31, 2012
Take or Pay Contracts [Member]
USD ($)
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Dec. 31, 2013
Customer Supplemental Payments [Member]
U.S. Iron Ore [Member]
USD ($)
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Dec. 31, 2012
Customer Supplemental Payments [Member]
U.S. Iron Ore [Member]
USD ($)
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Dec. 31, 2013
Wisco [Member]
USD ($)
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Dec. 31, 2012
Wisco [Member]
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Dec. 31, 2011
Consolidated Thompson [Member]
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May 12, 2011
Consolidated Thompson [Member]
CAD
|
Dec. 31, 2012
Consolidated Thompson [Member]
Eastern Canadian Iron Ore [Member]
USD ($)
|
Dec. 31, 2013
Bloom Lake [Member]
USD ($)
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| Related Party Transaction [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Impairment of Tangible Assets | $ 145,100,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Impairment of Long-Lived Assets Held-for-use | 140,100,000 | 49,900,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Inventory Valuation Reserves | 63,400,000 | 29,800,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Business Acquisition, Share Price | 17.25 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions | 100.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Number Of Mines | 5 | 1 | 2 | 4 | 1 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Trading Day Window Determining Number of Common Shares Issuable on Conversion | 20 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Depositary Share Interest in a Share of 7% Series A Mandatory Convertible Preferred Stock, Class A | 0.025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Current Fiscal Year End Date | --12-31 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Deferred Revenue | 13,500,000 | 17,100,000 | 115,600,000 | 128,400,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Ownership Interest | 45.00% | 100.00% | 70.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Increase in Subsidiary or Equity Method Investee Percentage Ownership Acquired | 7.80% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Units Issued by CQIM to Bloom Lake for Acquisition of Noncontrolling Interest | 457,556 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Ownership interest, equity method investment | 0.00% | [1] | 30.00% | [1] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Total percentage of Amapa sold | 100.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Equity Method Investment, Other than Temporary Impairment | 67,600,000 | 365,400,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Proceeds from sale of economic interest (in AUD) | 4.00 | 141,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Estimated rehabilitation costs | 18,600,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Goodwill | 74,500,000 | 167,400,000 | 1,152,100,000 | 2,000,000 | 2,000,000 | 2,000,000 | 72,500,000 | 84,500,000 | 83,000,000 | 80,900,000 | 0 | 80,900,000 | 0 | 0 | 0 | 0 | 0 | 986,200,000 | 997,300,000 | |||||||||||||||||||||||||||||||||||||||||
| Reimbursement Revenue | 259,500,000 | 250,800,000 | 224,300,000 | 85,800,000 | 101,000,000 | 18,300,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Allowance for Doubtful Accounts Receivable | 8,100,000 | 8,100,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Provision for Doubtful Accounts | 0 | 9,000,000 | 5,900,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Quantity Of Finished Goods | 1,200,000 | 1,300,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Derivative, Policy, Percentage of Amount Permitted to be Hedged | 75.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Derivative, Policy, Minimum Percentage of Amount Permitted to be Hedged for Derivatives with Periods of up to Twelve Months | 40.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Derivative, Policy, Minimum Percentage of Amount Permitted to be Hedged for Derivatives with Periods of up to Fifteen Months | 10.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Deferred Revenue, Current | 12,800,000 | 12,800,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Deferred Revenue, Noncurrent | 102,800,000 | 115,600,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent | (100,000) | (18,500,000) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Discontinued Operation, Tax Effect of Discontinued Operation | 9,200,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Asset Impairment Charges | 250,800,000 | 1,049,900,000 | 27,800,000 | 16,000,000 | 154,600,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Impairment of Intangible Assets, Finite-lived | 9,500,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Noncontrolling Interest, Ownership Percentage by Parent | 79.00% | 100.00% | 100.00% | 82.80% | 75.00% | 82.80% | 75.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||||
| Subsidiary Or Equity Method Investee Percentage Ownership Acquired | 17.152% | 25.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Increase/Decrease in Equity for WISCO/Bloom Lake through Acquisition of Noncontrolling Interest | 314,800,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Increase to Cliffs' Shareholders Equity through Acquisition of Noncontrolling Interest | 314,800,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition | 45,100,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Change in Diluted EPS for Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition | $ 0.29 | $ 0.04 | $ 0.04 | $ 0.03 | $ 0.14 | $ 0.26 | $ 0.25 | $ 0.07 | ||||||||||||||||||||||||||||||||||||||||||||||||||||
| Goodwill, Impairment Loss | $ 80,900,000 | $ 1,000,000,000 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 1,000,000,000 | $ 997,300,000 | $ 2,700,000 | |||||||||||||||||||||||||||||||||||||||||||||||
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