Annual report pursuant to Section 13 and 15(d)

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details)

v3.3.1.900
DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Derivative [Line Items]          
Current Fiscal Year End Date   --12-31      
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net   $ (6,500,000) $ (28,200,000) $ (51,700,000)  
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net   (18,800,000) (31,000,000) (22,100,000)  
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net   5,500,000 161,400,000 141,100,000  
Accounts receivable, net   40,200,000 122,700,000    
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   0 (14,300,000) (4,100,000)  
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net   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)  
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member]          
Derivative [Line Items]          
Derivative, Notional Amount   0      
Foreign Exchange Contract [Member] | Other Nonoperating Income (Expense) [Member]          
Derivative [Line Items]          
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments       (600,000)  
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [1]   (3,600,000) (16,900,000)    
Foreign Exchange Contract [Member] | Product Revenues [Member]          
Derivative [Line Items]          
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net   (12,600,000) 0 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   (2,000,000) (13,900,000) (34,700,000)  
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 $ 6,300,000 (7,400,000) (13,200,000) (11,900,000)  
Australian Dollar Foreign Exchange Contract Hedge Designation [Member] | Designated as Hedging Instrument [Member]          
Derivative [Line Items]          
Derivative, Notional Amount   0 220,000,000    
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   0      
Australian Dollar Foreign Exchange Contracts Dedesignated [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      
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 0 (12,900,000)  
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)  
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] | 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) (100,000)  
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   27,100,000 187,800,000 149,200,000  
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]          
Derivative [Line Items]          
Derivative assets   5,800,000 63,200,000    
Provisional Pricing Arrangements [Member] | Product Revenues [Member]          
Derivative [Line Items]          
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net   (1,400,000) (9,500,000) (7,500,000)  
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | U S Iron Ore And Asia Pacific Iron Ore [Member] | Product Revenues [Member]          
Derivative [Line Items]          
Amount of gain/(loss) recognized in income on derivative   (1,400,000) (9,500,000) (7,500,000)  
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | U S Iron Ore And Asia Pacific Iron Ore [Member] | Other Current Assets [Member]          
Derivative [Line Items]          
Derivative assets   2,000,000 0    
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | U S Iron Ore And Asia Pacific Iron Ore [Member] | Other Current Liabilities [Member]          
Derivative [Line Items]          
Derivative liabilities   3,400,000 9,500,000    
$500 Million 3.95% 2018 Senior Notes [Member]          
Derivative [Line Items]          
Debt Instrument, Face Amount   500,000,000 500,000,000.0    
Corporate [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) $ (1,900,000)  
Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts     0    
Corporate [Member] | Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member]          
Derivative [Line Items]          
Derivative, Notional Amount   $ 0 183,000,000    
Corporate [Member] | Foreign Exchange Contract [Member] | Cost of Sales [Member]          
Derivative [Line Items]          
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments     3,300,000    
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net     $ (7,300,000)    
[1] At December 31, 2014 and 2013, the location of the Gain (Loss) Recognized in Income on Derivative for Foreign Exchange Contracts was Cost of goods sold and operating expenses.