Basis Points

Name:	clf_BasisPoints
Namespace Prefix:	clf
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Transfers Into Level Three

+ Details

Name:	clf_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevelThree
Namespace Prefix:	clf
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Financial assets or liabilities measured at fair value on a non-recurring basis

+ Details

Name:	clf_FinancialAssetsOrLiabilitiesMeasuredAtFairValueOnNonRecurringBasis
Namespace Prefix:	clf
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee.

+ Details

Name:	clf_PercentageOfOwnershipInterests
Namespace Prefix:	clf
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Risk Free Discount Rate

+ Details

Name:	clf_RiskFreeDiscountRate
Namespace Prefix:	clf
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ Details

Name:	us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the transfers of assets or liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueLevel1ToLevel2TransfersAmount
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The aggregate of amounts due from customers or clients more than one year from the balance sheet date, for goods or services that have been delivered or sold in the normal course of business and an amount representing an agreement for an unconditional promise by the maker to pay the Company (holder) a definite sum of money at a future date more than one year from the balance sheet date, reduced to their estimated net realizable fair value by an allowance established by the Company of the amount it deems uncertain of collection and net of any write-downs taken for collection uncertainty on the part of the holder, respectively.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 17

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermAccountsNotesAndLoansReceivableNetNoncurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. Includes disclosure of claims held for amounts due a company. Examples include trade accounts receivables, notes receivables, loans receivables.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3, 4

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_ReceivablesFairValueDisclosure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair Value Of Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		9 Months Ended			12 Months Ended			12 Months Ended
	Sep. 30, 2009	Jun. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Dec. 31, 2010 Empire [Member]	Sep. 30, 2011 Empire [Member]	Dec. 31, 2002 Empire [Member]	Dec. 31, 2010 U.S. Iron Ore [Member]	Dec. 31, 2013 U.S. Iron Ore [Member]	Sep. 30, 2011 U.S. Iron Ore [Member]
Financial assets or liabilities measured at fair value on a non-recurring basis						$ 0
Fair value transfers amount between Level 1 and Level 2				0
Interest rate on long term receivable	9
Percent ownership interest							79.00%		46.70%
Transfers out of Level 3			161.8	20.0	161.8
Long-term receivables							32.8	28.1	120.0	22.3	22.3	22.3
Fair value of the receivable							38.9	32.7		19.5		20.5
Estimated credit-adjusted risk-free interest rate							3.10%			4.70%
Basis points	350
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, transfers out of Level 3		$ 20.0	$ (161.8)