Annual report pursuant to Section 13 and 15(d)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Revenue Reimbursement) (Details)

v2.4.1.9
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Revenue Reimbursement) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Reimbursement Revenue $ 392.9us-gaap_ReimbursementRevenue $ 344.8us-gaap_ReimbursementRevenue $ 351.8us-gaap_ReimbursementRevenue
U.S. Iron Ore [Member]      
Reimbursement Revenue 271.0us-gaap_ReimbursementRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		259.5us-gaap_ReimbursementRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		250.8us-gaap_ReimbursementRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
U.S. Iron Ore [Member] | Freight Revenue [Member]      
Reimbursement Revenue 163.0us-gaap_ReimbursementRevenue
/ clf_ReimbursementRevenueByTypeAxis
= clf_FreightRevenueMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		177.3us-gaap_ReimbursementRevenue
/ clf_ReimbursementRevenueByTypeAxis
= clf_FreightRevenueMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		142.0us-gaap_ReimbursementRevenue
/ clf_ReimbursementRevenueByTypeAxis
= clf_FreightRevenueMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
U.S. Iron Ore [Member] | Co-venturer [Member]      
Reimbursement Revenue $ 108.0us-gaap_ReimbursementRevenue
/ clf_ReimbursementRevenueByTypeAxis
= us-gaap_CoVenturerMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		$ 82.2us-gaap_ReimbursementRevenue
/ clf_ReimbursementRevenueByTypeAxis
= us-gaap_CoVenturerMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		$ 108.8us-gaap_ReimbursementRevenue
/ clf_ReimbursementRevenueByTypeAxis
= us-gaap_CoVenturerMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember