Annual report pursuant to Section 13 and 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS (Carrying Value And Fair Value Of Financial Instruments Disclosure) (Details)

v2.4.1.9
FAIR VALUE OF FINANCIAL INSTRUMENTS (Carrying Value And Fair Value Of Financial Instruments Disclosure) (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Long-term debt:    
Term loan, carrying value $ 2,984,100,000us-gaap_LongTermDebt $ 3,043,500,000us-gaap_LongTermDebt
Total long-term debt, carrying value 2,962,300,000us-gaap_LongTermDebtNoncurrent 3,022,600,000us-gaap_LongTermDebtNoncurrent
Seven Hundred Million Four Point Eight Seven Five Two Thousand Twenty-one Senior Note [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt Instrument, Face Amount 700,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember 		700,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember
Long-term debt:    
Term loan, carrying value 689,500,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember 		[1] 699,400,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember 		[1]
Senior Notes - $1.3 Billion [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt Instrument, Face Amount 1,300,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOnePointThreeBillionMember 		1,300,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOnePointThreeBillionMember
Senior Notes - $400 Million [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt Instrument, Face Amount 400,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		400,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember
Long-term debt:    
Term loan, carrying value 393,700,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		[2] 398,400,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		[2]
$500 Million 3.95% 2018 Senior Notes [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt Instrument, Face Amount 500,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		500,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember
Long-term debt:    
Term loan, carrying value 477,400,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		[3] 496,500,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		[3]
Revolving Credit Facility [Member]    
Long-term debt:    
Revolving loan, carrying value 0us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		[4] 0us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		[4]
Equipment Loans [Member]    
Long-term debt:    
Term loan, carrying value 140,800,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_EquipmentLoansMember 		161,700,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_EquipmentLoansMember
Interest Rate Swap [Member]    
Long-term debt:    
Fair Value Adjustment to Interest Rate Hedge 2,800,000clf_FairValueAdjustmenttoInterestRateHedge
/ us-gaap_DebtInstrumentAxis
= us-gaap_InterestRateSwapMember 		(2,100,000)clf_FairValueAdjustmenttoInterestRateHedge
/ us-gaap_DebtInstrumentAxis
= us-gaap_InterestRateSwapMember
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]    
Long-term debt:    
Total long-term debt, fair value 1,733,200,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember 		3,217,700,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Seven Hundred Million Four Point Eight Seven Five Two Thousand Twenty-one Senior Note [Member]    
Long-term debt:    
Debt Instrument, Fair Value Disclosure 367,300,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember 		718,200,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Senior Notes - $1.3 Billion [Member]    
Long-term debt:    
Debt Instrument, Fair Value Disclosure 704,000,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOnePointThreeBillionMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember 		1,404,900,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOnePointThreeBillionMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Senior Notes - $400 Million [Member]    
Long-term debt:    
Debt Instrument, Fair Value Disclosure 228,100,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember 		432,100,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | $500 Million 3.95% 2018 Senior Notes [Member]    
Long-term debt:    
Debt Instrument, Fair Value Disclosure 312,000,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember 		523,800,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Revolving Credit Facility [Member]    
Long-term debt:    
Revolving loan, fair value 0us-gaap_LinesOfCreditFairValueDisclosure
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember 		0us-gaap_LinesOfCreditFairValueDisclosure
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Equipment Loans [Member]    
Long-term debt:    
Debt Instrument, Fair Value Disclosure 119,000,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_EquipmentLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember 		140,800,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_EquipmentLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]    
Long-term debt:    
Fair Value Adjustment to Interest Rate Hedge 2,800,000clf_FairValueAdjustmenttoInterestRateHedge
/ us-gaap_DebtInstrumentAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember 		(2,100,000)clf_FairValueAdjustmenttoInterestRateHedge
/ us-gaap_DebtInstrumentAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_PortionAtFairValueFairValueDisclosureMember
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]    
Long-term debt:    
Total long-term debt, carrying value 2,962,300,000us-gaap_LongTermDebtNoncurrent
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember 		3,022,600,000us-gaap_LongTermDebtNoncurrent
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Seven Hundred Million Four Point Eight Seven Five Two Thousand Twenty-one Senior Note [Member]    
Long-term debt:    
Senior notes, carrying value 689,500,000us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember 		699,400,000us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Senior Notes - $1.3 Billion [Member]    
Long-term debt:    
Senior notes, carrying value 1,279,900,000us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOnePointThreeBillionMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember 		1,289,600,000us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOnePointThreeBillionMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Senior Notes - $400 Million [Member]    
Long-term debt:    
Senior notes, carrying value 393,700,000us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember 		398,400,000us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | $500 Million 3.95% 2018 Senior Notes [Member]    
Long-term debt:    
Senior notes, carrying value 477,400,000us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember 		496,500,000.0us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Revolving Credit Facility [Member]    
Long-term debt:    
Revolving loan, carrying value 0us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember 		0us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Equipment Loans [Member]    
Long-term debt:    
Term loan, carrying value 119,000,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_EquipmentLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember 		140,800,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= clf_EquipmentLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]    
Long-term debt:    
Carrying Value of Fair Value Adjustment to Interest Rate Hedge $ 2,800,000clf_CarryingValueofFairValueAdjustmenttoInterestRateHedge
/ us-gaap_DebtInstrumentAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember 		$ (2,100,000)clf_CarryingValueofFairValueAdjustmenttoInterestRateHedge
/ us-gaap_DebtInstrumentAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
[1] During the fourth quarter of 2014, we purchased $10.0 million of outstanding 4.875 percent senior notes that were trading at a discount of 40.5 percent which resulted in a gain on the extinguishment of debt of $4.1 million. As of December 31, 2014, the $700.0 million 4.875 percent senior notes were recorded at a par value of $690.0 million less unamortized discounts of $0.5 million, based on an imputed interest rate of 4.88 percent. As of December 31, 2013, the $700.0 million 4.875 percent senior notes were recorded at a par value of $700.0 million less unamortized discounts of $0.6 million, based on an imputed interest rate of 4.88 percent.
[2] During the fourth quarter of 2014, we purchased $5.0 million of outstanding 5.90 percent senior notes that were trading at a discount of 38.125 percent which resulted in a gain on the extinguishment of debt of $1.9 million. As of December 31, 2014, the $400.0 million 5.90 percent senior notes were recorded at a par value of $395.0 million less unamortized discounts of $1.3 million, based on an imputed interest rate of 5.98 percent. As of December 31, 2013, the $400.0 million 5.90 percent senior notes were recorded at a par value of $400.0 million less unamortized discounts of $1.6 million, based on an imputed interest rate of 5.98 percent.
[3] During the fourth quarter of 2014, we purchased $20.0 million of outstanding 3.95 percent senior notes that were trading at a discount of 30.875 percent which resulted in a gain on the extinguishment of debt of $6.2 million. As of December 31, 2014, the $500.0 million 3.95 percent senior notes were recorded at a par value of $480.0 million less unamortized discounts of $2.6 million, based on an imputed interest rate of 5.17 percent. As of December 31, 2013, the $500.0 million 3.95 percent senior notes were recorded at a par value of $500.0 million less unamortized discounts of $3.5 million, based on an imputed interest rate of 4.14 percent.
[4] As of December 31, 2014 and 2013, no revolving loans were drawn under the credit facility. We had total availability of $1.125 billion and $1.75 billion on our credit facility as of December 31, 2014 and 2013, respectively. Additionally, as of December 31, 2014 and December 31, 2013, the principal amount of letter of credit obligations totaled $149.5 million and $8.4 million, respectively, thereby reducing available borrowing capacity to $1.0 billion and $1.7 billion for each period, respectively.