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Quarterly report pursuant to Section 13 or 15(d)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Investments In Unconsolidated Ventures) (Details)

v2.4.1.9
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Investments In Unconsolidated Ventures) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Schedule of Equity Method Investments [Line Items] Ìý Ìý
Investment $ 3.4us-gaap_EquityMethodInvestments $ 4.1us-gaap_EquityMethodInvestments
Other Noncurrent Liabilities [Member] | Hibbing [Member] Ìý Ìý
Schedule of Equity Method Investments [Line Items] Ìý Ìý
Investment Ìý 3.1us-gaap_EquityMethodInvestments
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherNoncurrentLiabilitiesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember
Other Noncurrent Assets [Member] | Hibbing [Member] Ìý Ìý
Schedule of Equity Method Investments [Line Items] Ìý Ìý
Ownership interest, equity method investment 23.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherNoncurrentAssetsMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember 		Ìý
Investment 2.5us-gaap_EquityMethodInvestments
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherNoncurrentAssetsMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember 		Ìý
Other Noncurrent Assets [Member] | Other Equity Investees [Member] Ìý Ìý
Schedule of Equity Method Investments [Line Items] Ìý Ìý
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