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Quarterly report pursuant to Section 13 or 15(d)

SEGMENT REPORTING Segment Reporting (Summary of Assets by Segment) (Details)

v2.4.1.9
SEGMENT REPORTING Segment Reporting (Summary of Assets by Segment) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Segment Reporting Information [Line Items] Ìý Ìý
Assets $ 2,702.6us-gaap_Assets $ 3,164.0us-gaap_Assets
U.S. Iron Ore [Member] Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Assets 1,550.1us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		1,464.9us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Asia Pacific Iron Ore [Member] Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Assets 250.6us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		274.6us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
All Other Segments [Member] Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Assets 31.2us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		147.0us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember
Total Segment Assets [Member] Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Assets 1,831.9us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_OperatingSegmentsMember 		1,886.5us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_OperatingSegmentsMember
Corporate [Member] Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Assets 673.5us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateMember 		546.8us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateMember
Discontinued Operations [Member] Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Disposal Group, Including Discontinued Operation, Assets $ 197.2us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_SegmentDiscontinuedOperationsMember 		$ 730.7us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_SegmentDiscontinuedOperationsMember