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Annual report pursuant to Section 13 and 15(d)

DEBT AND CREDIT FACILITIES (Narrative) (Details)

v2.4.1.9
DEBT AND CREDIT FACILITIES (Narrative) (Details)
 0 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 0 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Aug. 11, 2011
Term Loan [Member]
USD ($)
May 27, 2010
Amapa's Debt [Member]
USD ($)
Dec. 31, 2014
Senior Notes - $400 Million [Member]
USD ($)
Dec. 31, 2013
Senior Notes - $400 Million [Member]
USD ($)
Dec. 31, 2014
Senior Notes - $400 Million [Member]
Maximum [Member]
Dec. 31, 2014
Senior Notes - $400 Million [Member]
Minimum [Member]
Dec. 31, 2014
Five Hundred Million Four Point Eight Zero Percent Senior Note [Member]
USD ($)
Dec. 31, 2013
Five Hundred Million Four Point Eight Zero Percent Senior Note [Member]
USD ($)
Dec. 31, 2014
Five Hundred Million Six Point Two Five Percent Two Thousand And Forty [Member]
USD ($)
Dec. 31, 2014
Senior Notes10 Year Tranche [Member]
USD ($)
Dec. 31, 2014
Seven Hundred Million Four Point Eight Seven Five Two Thousand Twenty-one Senior Note [Member]
USD ($)
Dec. 31, 2013
Seven Hundred Million Four Point Eight Seven Five Two Thousand Twenty-one Senior Note [Member]
USD ($)
Sep. 22, 2010
Revolving Credit Facility [Member]
USD ($)
Dec. 31, 2014
Revolving Credit Facility [Member]
USD ($)
Dec. 31, 2013
Revolving Credit Facility [Member]
USD ($)
Sep. 30, 2014
Revolving Credit Facility [Member]
USD ($)
Dec. 31, 2012
$270 Million Senior Notes [Member]
USD ($)
Dec. 31, 2012
Series Two Thousand And Eight Tranche B [Member]
USD ($)
Dec. 31, 2014
Senior Notes Five Hundred Million [Member]
Dec. 31, 2014
Senior Notes Five Hundred Million [Member]
Maximum [Member]
Dec. 31, 2014
Senior Notes Five Hundred Million [Member]
Minimum [Member]
Dec. 31, 2014
Five Hundred Million Three Point Nine Five Two Thousand Eighteen Senior Note [Member]
USD ($)
Dec. 31, 2013
Five Hundred Million Three Point Nine Five Two Thousand Eighteen Senior Note [Member]
USD ($)
Dec. 31, 2014
Equipment Loans [Member]
USD ($)
Dec. 31, 2014
Line of Credit [Member]
USD ($)
Dec. 31, 2014
Line of Credit [Member]
AUD
Dec. 31, 2013
Line of Credit [Member]
USD ($)
Dec. 31, 2013
Line of Credit [Member]
AUD
Dec. 31, 2014
Senior Notes30 Year Tranche [Member]
USD ($)
Dec. 31, 2014
Senior Notes One Billion Two Thousand Eleven Offering [Member]
USD ($)
Dec. 31, 2014
Senior Notes One Billion Two Thousand Eleven Offering [Member]
Maximum [Member]
Dec. 31, 2014
Senior Notes One Billion Two Thousand Eleven Offering [Member]
Minimum [Member]
Dec. 31, 2014
Senior Notes One Billion Two Thousand Ten Offering [Member]
USD ($)
Dec. 31, 2014
Senior Notes One Billion Two Thousand Ten Offering [Member]
Maximum [Member]
Dec. 31, 2014
Senior Notes One Billion Two Thousand Ten Offering [Member]
Minimum [Member]
Line of Credit Facility [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
liquidity test Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý $ 400,000,000clf_Liquiditytest
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Stock Repurchase Program, Authorized Amount 200,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1 Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Debt Instrument, Repurchased Face Amount Ìý Ìý Ìý Ìý 5,000,000us-gaap_DebtInstrumentRepurchasedFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		Ìý Ìý Ìý 10,000,000us-gaap_DebtInstrumentRepurchasedFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionFourPointEightZeroPercentSeniorNoteMember 		Ìý Ìý Ìý 10,000,000us-gaap_DebtInstrumentRepurchasedFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 20,000,000us-gaap_DebtInstrumentRepurchasedFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Long-term Line of Credit, Noncurrent Ìý Ìý 200,000,000us-gaap_LongTermLineOfCredit
/ us-gaap_DebtInstrumentAxis
= clf_TermLoanMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Repayments of Debt Ìý Ìý Ìý 100,800,000us-gaap_RepaymentsOfDebt
/ us-gaap_DebtInstrumentAxis
= clf_AmapasDebtMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 350,000,000us-gaap_RepaymentsOfDebt
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		Ìý Ìý Ìý 270,000,000us-gaap_RepaymentsOfDebt
/ us-gaap_DebtInstrumentAxis
= clf_SeriesTwoThousandAndEightTrancheMember 		55,000,000us-gaap_RepaymentsOfDebt
/ us-gaap_DebtInstrumentAxis
= clf_SeriesTwoThousandAndEightTrancheBMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Revolving credit facility, borrowing capacity Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 2,500,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		3,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		26,800,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		30,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Debt Instrument, Face Amount Ìý Ìý Ìý Ìý 400,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		400,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		Ìý Ìý 500,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionFourPointEightZeroPercentSeniorNoteMember 		500,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionFourPointEightZeroPercentSeniorNoteMember 		500,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionSixPointTwoFivePercentTwoThousandAndFortyMember 		Ìý 700,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember 		700,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 500,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		500,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		Ìý Ìý Ìý Ìý Ìý 300,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_ThreeHundredMillionSixPointTwoFivePercentTwoThousandAndFortyMember 		1,000,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOneBillionTwoThousandElevenOfferingMember 		Ìý Ìý 1,000,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOneBillionTwoThousandTenOfferingMember 		Ìý Ìý
Financial covenant, interest coverage ratio Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 3.5clf_CoverageRatioOfEarningsBeforeInterestTaxDepreciationAndAmortizationToTotalInterestExpense
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		2.5clf_CoverageRatioOfEarningsBeforeInterestTaxDepreciationAndAmortizationToTotalInterestExpense
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Credit facility, amount outstanding Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 0us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		[1] 0us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		[1] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 1,200,000us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		1,500,000us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		20,500,000us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		23,000,000us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Credit facility remaining capacity Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 1,000,000,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		1,700,000,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 1,300,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		1,500,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		6,300,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		7,000,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= us-gaap_LineOfCreditMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Letters of credit outstanding Ìý 48,000,000us-gaap_LettersOfCreditOutstandingAmount Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Time Period During Which Senior Notes May Be Redeemed at Company's Option, Number of Days From When Prior Notice Sent to Holders Ìý Ìý Ìý Ìý Ìý Ìý 60 days 30 days Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 60 days 30 days Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 60 days 30 days Ìý 60 days 30 days
Note Redemption Price, Percent of Principal Amount to be Redeemed Ìý Ìý Ìý Ìý 100.00%clf_NoteRedemptionPricePercentOfPrincipalAmountToBeRedeemed
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 100.00%clf_NoteRedemptionPricePercentOfPrincipalAmountToBeRedeemed
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesFiveHundredMillionMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 100.00%clf_NoteRedemptionPricePercentOfPrincipalAmountToBeRedeemed
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOneBillionTwoThousandElevenOfferingMember 		Ìý Ìý 100.00%clf_NoteRedemptionPricePercentOfPrincipalAmountToBeRedeemed
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOneBillionTwoThousandTenOfferingMember 		Ìý Ìý
Redemption Price, Percent Of Principal In The Event Of Change Of Control Ìý Ìý Ìý Ìý 101.00%clf_RedemptionPricePercentOfPrincipalInEventOfChangeOfControl
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 101.00%clf_RedemptionPricePercentOfPrincipalInEventOfChangeOfControl
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesFiveHundredMillionMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 101.00%clf_RedemptionPricePercentOfPrincipalInEventOfChangeOfControl
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesOneBillionTwoThousandElevenOfferingMember 		Ìý Ìý Ìý Ìý Ìý
Debt Instrument, Par Value 4,144,800,000clf_DebtInstrumentParValue 4,814,800,000clf_DebtInstrumentParValue Ìý Ìý 395,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		400,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		Ìý Ìý 490,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionFourPointEightZeroPercentSeniorNoteMember 		500,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionFourPointEightZeroPercentSeniorNoteMember 		Ìý Ìý 690,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember 		700,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember 		Ìý 1,125,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		1,750,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		1,250,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		Ìý Ìý Ìý Ìý Ìý 480,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		500,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		164,800,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= clf_EquipmentLoansMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Percentage of Stock to Pledge Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 65.00%clf_PercentageofStocktoPledge
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Total Funded Debt to Total Capitalization Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 0.45clf_TotalFundedDebttoTotalCapitalization
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Debt to Earnings Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 3.5clf_DebttoEarnings
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Limit on Increase in Interest Rate Above Initial Interest Rate, Based on Rating Events Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 2.00%clf_LimitOnIncreaseInInterestRateAboveInitialInterestRateBasedOnRatingEvents
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotesFiveHundredMillionMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Debt Instrument, Redemption Period, Time Period Prior to Maturity Date Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 3 months Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Note Redemption Price if Redemption Period is During Specified Time Period, Percent of Principal Amount to be Redeemed Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 100.00%clf_NoteRedemptionPriceIfRedemptionPeriodIsDuringSpecifiedTimePeriodPercentOfPrincipalAmountToBeRedeemed
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotes10YearTrancheMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Senior Notes, Noncurrent Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý $ 500,000,000us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionFourPointEightZeroPercentSeniorNoteMember 		Ìý Ìý $ 700,000,000us-gaap_SeniorLongTermNotes
/ us-gaap_DebtInstrumentAxis
= clf_SeniorNotes10YearTrancheMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Debt Instrument, Interest Rate, Stated Percentage Ìý Ìý Ìý Ìý 5.90%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		5.90%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= clf_FourHundredMillionFivePointNineZeroTwoThousandAndTwentySeniorNoteMember 		Ìý Ìý 4.80%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionFourPointEightZeroPercentSeniorNoteMember 		4.80%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionFourPointEightZeroPercentSeniorNoteMember 		Ìý Ìý 4.875%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= clf_SevenHundredMillionFourPointEightSevenFiveTwoThousandTwentyoneSeniorNoteMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 3.95%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Interest Rate Due to Rating Downgrades Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 5.70%clf_InterestRateDuetoRatingDowngrades
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
[1] As of DecemberÌý31, 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.