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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Investments In Unconsolidated Ventures) (Details) (USD $)
In Millions, unless otherwise specified |
Mar. 31, 2015
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Dec. 31, 2014
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| Schedule of Equity Method Investments [Line Items] | ||
| Investment | $ 3.4us-gaap_EquityMethodInvestments | $ 4.1us-gaap_EquityMethodInvestments |
| Other Noncurrent Liabilities [Member] | Hibbing [Member] | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Investment |
3.1us-gaap_EquityMethodInvestments / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherNoncurrentLiabilitiesMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_HibbingMember |
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| Other Noncurrent Assets [Member] | Hibbing [Member] | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Ownership interest, equity method investment |
23.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherNoncurrentAssetsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_HibbingMember |
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| Investment |
2.5us-gaap_EquityMethodInvestments / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherNoncurrentAssetsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_HibbingMember |
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| Other Noncurrent Assets [Member] | Other Equity Investees [Member] | ||
| Schedule of Equity Method Investments [Line Items] | ||
| Investment |
$ 0.9us-gaap_EquityMethodInvestments / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherNoncurrentAssetsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_OtherEquityInvesteesMember |
$ 1.0us-gaap_EquityMethodInvestments / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherNoncurrentAssetsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_OtherEquityInvesteesMember |
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- Definition
The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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