Cleveland-Cliffs Inc. Quarterly report pursuant to Section 13 or 15(d)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details)

v3.8.0.1

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Empire [Member]
Related Party Transaction [Line Items]
Increase in Ownership Equity	21.00%
Purchase of Noncontrolling Interest	$ 132.7
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%	79.00%
Noncontrolling Interest Purchase, Installment Amount	$ 44.2
Stockholders' Equity, Period Increase (Decrease)	16.0
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	$ 116.7	$ (132.7)
Tilden [Member]
Related Party Transaction [Line Items]
Increase in Ownership Equity	15.00%
Purchase of Noncontrolling Interest	$ 105.0
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	100.00%	85.00%
Stockholders' Equity, Period Increase (Decrease)	$ 89.1
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	15.9	$ (105.0)
Other Noncurrent Liabilities [Member] \| Empire [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest Purchase, Installment Amount	$ 44.2
Hibbing [Member] \| Other Noncurrent Assets [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment	23.00%	23.00%	23.00%
Hibbing [Member] \| Other Noncurrent Liabilities [Member]
Related Party Transaction [Line Items]
Equity Method Investments	$ 6.1	$ 6.1	$ 8.7

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Decrease in noncontrolling interest (for example, but not limited to, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares (interests) by the non-wholly owned subsidiary to the parent entity for other than cash, and a buyback of shares (interest) by the non-wholly owned subsidiary from the noncontrolling interests).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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The increase (decrease) in stockholders' equity during the period.

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