Cleveland-Cliffs Inc. Annual report pursuant to Section 13 and 15(d)

CAPITAL STOCK (Details)

CAPITAL STOCK (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				12 Months Ended			2 Months Ended	3 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 21, 2013	Feb. 11, 2013	Nov. 19, 2014	Nov. 03, 2014	Aug. 01, 2014	Feb. 03, 2014	Nov. 01, 2013	Aug. 01, 2013	Mar. 20, 2013	Sep. 02, 2014	Jun. 03, 2014	Mar. 03, 2014	Dec. 02, 2013	Sep. 03, 2013	Jun. 03, 2013	Mar. 01, 2013
Class of Stock [Line Items]
Depositary Share Interest in a Share of 7% Series A Mandatory Convertible Preferred Stock, Class A					0.025
Common Stock, Par or Stated Value Per Share	$ 0.125				$ 0.125	$ 0.125
Trading Day Window Determining Number of Common Shares Issuable on Conversion					20
Net proceeds from issuance of Series A, Mandatory Convertible Preferred Stock, Class A					$ 0	$ 709.4	$ 0
Dividends, Preferred Stock	12.8us-gaap_DividendsPreferredStock	12.8us-gaap_DividendsPreferredStock	12.8us-gaap_DividendsPreferredStock	12.8us-gaap_DividendsPreferredStock	51.2us-gaap_DividendsPreferredStock	48.7us-gaap_DividendsPreferredStock	0us-gaap_DividendsPreferredStock
Common shares, issued (in shares)	159,546,224us-gaap_CommonStockSharesIssued				159,546,224us-gaap_CommonStockSharesIssued	159,546,224us-gaap_CommonStockSharesIssued
Net proceeds from issuance of common shares					0	285.3	0
Over Allotment Option [Member]
Class of Stock [Line Items]
Common shares, issued (in shares)								1,350,000
Preferred Class A [Member]
Class of Stock [Line Items]
Series A Mandatory Convertible Preferred Stock, Class A, Percentage					7.00%
Preferred Stock, Liquidation Preference Per Share	$ 1,000				$ 1,000	$ 1,000
Dividends payable, per share										$ 17.50	$ 17.5000	$ 0.44	$ 0.44	$ 0.44	$ 17.50	$ 13.6111
Dividends, Preferred Stock	$ 12.8				$ 51.2
Issuance of common shares, public offering (in shares)								731,250
Closing price per share (in usd per share)								$ 25
Common Stock [Member]
Class of Stock [Line Items]
Dividends payable, per share																	$ 0.150	$ 0.150	$ 0.150	$ 0.150	$ 0.150	$ 0.15	$ 0.15
Percentage increase (decrease) in dividends payable									76.00%
Issuance of common shares, public offering (in shares)								10,350,000
Common shares, issued (in shares)								9,000,000
Closing price per share (in usd per share)								$ 29.00
Common Stock [Member] \| Minimum [Member]
Class of Stock [Line Items]
Convertible Preferred Stock, Shares Issued upon Conversion	28.1480				28.1480
Convertible Preferred Stock, Shares Issued Upon Conversion per Depositary Share	0.7037				0.7037
Number of Common Shares Mandatory Convertible Stock Converts to on February 1, 2016	20,600,000				20,600,000
Common Stock [Member] \| Maximum [Member]
Class of Stock [Line Items]
Convertible Preferred Stock, Shares Issued upon Conversion	34.4840				34.4840
Number of Common Shares Mandatory Convertible Stock Converts to on February 1, 2016	25,200,000				25,200,000
Common Stock from when Mandatory Convertible Preferred Stock Converts on February 1, 2016 [Member]
Class of Stock [Line Items]
Common Stock, Par or Stated Value Per Share	$ 0.125				$ 0.125
Depositary Shares [Member]
Class of Stock [Line Items]
Depositary Share Offering included in Depositary Share Issuance								27,000,000
Number of Shares included in Depositary Share Issuance due to Exercise of								2,250,000
Preferred Stock, Liquidation Preference Per Share	$ 25				$ 25
Dividends payable, per share										$ 0.44	$ 0.44	$ 17.5000	$ 17.5000	$ 17.5000	$ 0.44	$ 0.34
Issuance of common shares, public offering (in shares)								29,250,000