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

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details)

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details) (USD $)	12 Months Ended			9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013
Derivative [Line Items]
Current Fiscal Year End Date	--12-31
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ (28,200,000)	$ (51,700,000)	$ 25,600,000
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(31,000,000)	(22,100,000)	18,100,000
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	159,100,000	141,400,000	163,200,000
Accounts receivable, net	205,600,000us-gaap_AccountsReceivableNetCurrent	270,000,000us-gaap_AccountsReceivableNetCurrent
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	(14,300,000)	(4,100,000)	0
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member] \| Cost of Sales [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(17,700,000)	(1,900,000)	0
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	0
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] \| Not Designated as Hedging Instrument [Member] \| Accumulated Other Comprehensive Income (Loss) [Member]
Derivative [Line Items]
Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts	0
Foreign Exchange Contract [Member] \| Cost of Sales [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(16,900,000)		0
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	(13,900,000)	(34,700,000)	20,200,000
Australian Dollar Foreign Exchange Contract Hedge Designation [Member] \| Product Revenues [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(13,200,000)	(11,900,000)	14,800,000
Australian Dollar Foreign Exchange Contract Hedge Designation [Member] \| Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	220,000,000	323,000,000
Australian Dollar Foreign Exchange Contract Hedge Designation [Member] \| Designated as Hedging Instrument [Member] \| Accumulated Other Comprehensive Income (Loss) [Member]
Derivative [Line Items]
Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts	(15,100,000)
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	0	(12,900,000)	6,700,000
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member] \| Cost of Sales [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	(8,200,000)	3,300,000
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member] \| Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	0	285,900,000
Interest Rate Swap [Member] \| Other Nonoperating Income (Expense) [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net	300,000			100,000
Interest Rate Swap [Member] \| Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	250,000,000
Treasury Lock [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net			(1,300,000)
Treasury Lock [Member] \| Other Nonoperating Income (Expense) [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(100,000)	(100,000)	0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0	0	(400,000)
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	(100,000)
Treasury Lock [Member] \| Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount			200,000,000
Treasury Lock [Member] \| Designated as Hedging Instrument [Member] \| Accumulated Other Comprehensive Income (Loss) [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net		(1,300,000)
Customer Supply Agreement [Member] \| Not Designated as Hedging Instrument [Member] \| Product Revenues [Member]
Derivative [Line Items]
Amount of gain/(loss) recognized in income on derivative	187,800,000	149,200,000	171,400,000
Customer Supply Agreement [Member] \| Not Designated as Hedging Instrument [Member] \| Other Current Assets [Member]
Derivative [Line Items]
Derivative assets	63,200,000	55,800,000
Provisional Pricing Arrangements [Member] \| Product Revenues [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(11,800,000)	(7,200,000)	(7,800,000)
Provisional Pricing Arrangements [Member] \| Not Designated as Hedging Instrument [Member] \| U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member] \| Product Revenues [Member]
Derivative [Line Items]
Amount of gain/(loss) recognized in income on derivative	(11,800,000)	(7,200,000)
Provisional Pricing Arrangements [Member] \| Not Designated as Hedging Instrument [Member] \| U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member] \| Other Current Assets [Member]
Derivative [Line Items]
Derivative assets	0	3,100,000
Provisional Pricing Arrangements [Member] \| Not Designated as Hedging Instrument [Member] \| U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member] \| Other Current Liabilities [Member]
Derivative [Line Items]
Derivative liabilities	11,800,000	10,300,000
Provisional Pricing Arrangements [Member] \| Not Designated as Hedging Instrument [Member] \| U.S. Iron Ore and Eastern Canadian Iron Ore [Member] \| Product Revenues [Member]
Derivative [Line Items]
Amount of gain/(loss) recognized in income on derivative			(7,800,000)
$500 Million 3.95% 2018 Senior Notes [Member]
Derivative [Line Items]
Debt Instrument, Face Amount	500,000,000	500,000,000.0
Bloom Lake [Member] \| Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(9,900,000)
Bloom Lake [Member] \| Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount	183,000,000
Bloom Lake [Member] \| Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] \| Not Designated as Hedging Instrument [Member] \| Accumulated Other Comprehensive Income (Loss) [Member]
Derivative [Line Items]
Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts	0
Bloom Lake [Member] \| Foreign Exchange Contract [Member] \| Cost of Sales [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(7,300,000)
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] \| Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(500,000)
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] \| Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		74,800,000
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] \| Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] \| Not Designated as Hedging Instrument [Member] \| Accumulated Other Comprehensive Income (Loss) [Member]
Derivative [Line Items]
Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts	0
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] \| Foreign Exchange Contract [Member] \| Cost of Sales [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	3,300,000	(600,000)
Wabush [Member] \| Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		$ (1,900,000)