Quarterly report pursuant to Section 13 or 15(d)

DEBT AND CREDIT FACILITIES DEBT AND CREDIT FACILITIES (Schedule of Debt Maturities) (Details)

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DEBT AND CREDIT FACILITIES DEBT AND CREDIT FACILITIES (Schedule of Debt Maturities) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Debt Disclosure [Abstract]  
Debt Maturities Remainder 2015 $ 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear
Debt Maturities 2016 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
Debt Maturities 2017 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
Debt Maturities 2018 436.0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
Debt Maturities 2019 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
Debt Maturities 2020 1,719.5us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
Debt Maturities 2021 and After 916.0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
Long-term Debt, Maturities, Total $ 3,071.5clf_LongTermDebtMaturitiesTotal