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Quarterly report pursuant to Section 13 or 15(d)

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details)

v2.4.1.9
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Loss Contingencies [Line Items] Ìý Ìý
Environmental $ 3.7us-gaap_AccrualForEnvironmentalLossContingencies $ 5.5us-gaap_AccrualForEnvironmentalLossContingencies
Mine Reclamation and Closing Liability, current and noncurrent 165.3clf_MineReclamationAndClosingLiabilityCurrentAndNoncurrent 165.3clf_MineReclamationAndClosingLiabilityCurrentAndNoncurrent
Total environmental and mine closure obligations 169.0clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrentAndNoncurrent 170.8clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrentAndNoncurrent
Less current portion 3.4clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrent 5.2clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrent
Long term environmental and mine closure obligations 165.6clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityNoncurrent 165.6clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityNoncurrent
U.S. Iron Ore [Member] | Owned Or Operating Facilities [Member] Ìý Ìý
Loss Contingencies [Line Items] Ìý Ìý
Mine Reclamation and Closing Liability, current and noncurrent 121.8clf_MineReclamationAndClosingLiabilityCurrentAndNoncurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= clf_OwnedOrOperatingFacilitiesMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
120.9clf_MineReclamationAndClosingLiabilityCurrentAndNoncurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= clf_OwnedOrOperatingFacilitiesMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Asia Pacific Iron Ore [Member] | Owned Or Operating Facilities [Member] Ìý Ìý
Loss Contingencies [Line Items] Ìý Ìý
Mine Reclamation and Closing Liability, current and noncurrent 20.3clf_MineReclamationAndClosingLiabilityCurrentAndNoncurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= clf_OwnedOrOperatingFacilitiesMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
21.5clf_MineReclamationAndClosingLiabilityCurrentAndNoncurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= clf_OwnedOrOperatingFacilitiesMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
LTV Steel Mining Company [Member] | Previously Owned Or Operating Facilities [Member] Ìý Ìý
Loss Contingencies [Line Items] Ìý Ìý
Mine Reclamation and Closing Liability, current and noncurrent $ 23.2clf_MineReclamationAndClosingLiabilityCurrentAndNoncurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= clf_PreviouslyOwnedOrOperatingFacilitiesMember
/ clf_MineClosureAxis
= clf_LTVSteelMiningCompanyMember
$ 22.9clf_MineReclamationAndClosingLiabilityCurrentAndNoncurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= clf_PreviouslyOwnedOrOperatingFacilitiesMember
/ clf_MineClosureAxis
= clf_LTVSteelMiningCompanyMember