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v3.3.1.900

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) T in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2015 USD ($) Facility T | Dec. 31, 2014 USD ($) T | Dec. 31, 2013 USD ($) shares | Jul. 10, 2012
Related Party Transaction [Line Items] |  |  |  |
Deferred Tax Assets, Gross, Current |  | $ 23,700,000 |  |
Tangible Asset Impairment Charges |  | 537,800,000 |  |
Inventory Valuation Reserves | $ 31,800,000 | 16,000,000 |  |
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 |  |  |
Goodwill | $ 2,000,000 | 2,000,000 | $ 74,500,000 |
Freight and venture partners' cost reimbursements | 180,900,000 | 278,000,000 | 259,000,000 |
Allowance for Doubtful Accounts Receivable | 7,100,000 | 0 |  |
Provision for Doubtful Accounts | $ 7,100,000 |  | 0.0 |
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% |  |  |
Discontinued Operation, Tax Effect of Discontinued Operation | $ (6,000,000) | (1,216,000,000) | (184,500,000) |
Asset Impairment Charges | 3,300,000 | 635,500,000 | 14,300,000 |
Goodwill, Impairment Loss | 0 | 73,500,000 |  |
Impairment of Intangible Assets (Excluding Goodwill) |  | 13,800,000 |  |
Deferred Tax Liabilities, Gross, Current |  | 4,000,000 |  |
Unamortized Debt Issuance Expense | $ 29,100,000 | 16,800,000 |  |
Amapa [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Equity Method Investment, Other than Temporary Impairment |  |  | 67,600,000 |
U.S. Iron Ore [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Number Of Mines | Facility | 5 |  |  |
Goodwill | $ 2,000,000 | 2,000,000 | 2,000,000 |
Freight and venture partners' cost reimbursements | $ 157,300,000 | $ 271,000,000 | 259,500,000 |
Quantity Of Finished Goods | T | 1.3 | 1.4 |  |
Goodwill, Impairment Loss | $ 0 | $ 0 |  |
Asia Pacific [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Freight and venture partners' cost reimbursements | $ 23,600,000 | 6,900,000 |  |
Asia Pacific Iron Ore [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Number Of Mines | Facility | 1 |  |  |
Goodwill | $ 0 | 0 | $ 72,500,000 |
Goodwill, Impairment Loss | $ 0 | 73,500,000 |  |
Sonoma [Member] | Asia Pacific Coal [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Ownership Interest |  |  |  | 45.00%
Empire [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Noncontrolling Interest, Ownership Percentage by Parent | 79.00% |  |  |
Bloom Lake [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Noncontrolling Interest, Ownership Percentage by Parent |  |  | 82.80% |
Investments in Ventures [Member] | Amapa [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Ownership interest, equity method investment |  |  | 30.00% |
Low Volatile Metallurgical Coal Mines [Member] | North American Coal [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Number Of Mines | Facility | 2 |  |  |
Take or Pay Contracts [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Deferred Revenue |  | 29,300,000 |  |
Customer Supplemental Payments [Member] | U.S. Iron Ore [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Deferred Revenue | $ 89,900,000 | 102,800,000 |  |
Deferred Revenue, Current | 12,800,000 | 12,800,000 |  |
Deferred Revenue, Noncurrent | $ 77,100,000 | 90,000,000 |  |
Wisco [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Increase in Subsidiary or Equity Method Investee Percentage Ownership Acquired |  |  | 7.80% |
Units Issued by CQIM to Bloom Lake for Acquisition of Noncontrolling Interest | shares |  |  | 457,556 |
Subsidiary Or Equity Method Investee Percentage Ownership Acquired |  |  | 17.152% |
Increase/Decrease in Equity for WISCO/Bloom Lake through Acquisition of Noncontrolling Interest |  |  | $ 314,800,000 |
Bloom Lake [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Increase to Cliffs' Shareholders Equity through Acquisition of Noncontrolling Interest |  | 314,800,000 |  |
Minimum [Member] | Other Machinery and Equipment [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 10 years |  |  |
Minimum [Member] | Electric Power Facilities [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 10 years |  |  |
Minimum [Member] | Land Improvements [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 20 years |  |  |
Minimum [Member] | Equipment [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 3 years |  |  |
Maximum [Member] | Other Machinery and Equipment [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 45 years |  |  |
Maximum [Member] | Electric Power Facilities [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 45 years |  |  |
Maximum [Member] | Land Improvements [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 45 years |  |  |
Maximum [Member] | Equipment [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 20 years |  |  |
Short-term intercompany loan [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Foreign Currency Transaction Gain (Loss), before Tax | $ 11,500,000 | 19,700,000 | 33,000,000 |
Transaction Gains and Losses Resulting from Remeasurement [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Foreign Currency Transaction Gain (Loss), before Tax | 16,300,000 | 29,000,000 | 53,200,000 |
Cash and Cash Equivalents [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Foreign Currency Transaction Gain (Loss), before Tax | $ 1,500,000 | $ 10,600,000 | $ 20,400,000 |

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