Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details)

v3.2.0.727
DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2015
Mar. 31, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Dec. 31, 2014
Derivative [Line Items]            
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net $ (4.1)   $ 14.4 $ (7.9) $ 38.5  
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (7.8)   (6.6) (14.1) (19.4)  
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 0.0   (0.2) 0.0 (0.5)  
Interest Rate Swap [Member] | Other Nonoperating Income (Expense) [Member]            
Derivative [Line Items]            
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net     0.1   0.3  
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]            
Derivative [Line Items]            
Derivative, Notional Amount     250.0   250.0  
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 (1.0) $ (6.3) (3.7) (7.3) (12.8)  
Australian Dollar Foreign Exchange Contract Hedge Designation [Member] | Designated as Hedging Instrument [Member]            
Derivative [Line Items]            
Derivative, Notional Amount 10.0     10.0   $ 220.0
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 (0.9)     (0.9)    
Australian Dollar Foreign Exchange Contract Prior To De Designation [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 (5.7)     (5.7)    
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 0.0   (2.7) 0.0 (6.1)  
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member]            
Derivative [Line Items]            
Derivative, Notional Amount 0.0     0.0   0.0
Foreign Exchange Contract [Member] | Other Nonoperating Income (Expense) [Member]            
Derivative [Line Items]            
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [1] (3.4)   (2.4) 2.5 (3.3)  
Foreign Exchange Contract [Member] | Product Revenues [Member]            
Derivative [Line Items]            
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net [1] (9.7)   0.0 (9.7) 0.0  
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 0.4   34.3 10.5 62.0  
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Assets [Member]            
Derivative [Line Items]            
Derivative assets 7.5     7.5   63.2
Provisional Pricing Arrangements [Member] | Product Revenues [Member]            
Derivative [Line Items]            
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net 8.4   (17.5) (7.8) (20.2)  
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 8.4   (17.5) (7.8) (20.2)  
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | U S Iron Ore And Asia Pacific Iron Ore [Member] | Derivative Financial Instruments, Assets [Member]            
Derivative [Line Items]            
Derivative assets 0.2     0.2   0.0
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | U S Iron Ore And Asia Pacific Iron Ore [Member] | Derivative Financial Instruments, Liabilities [Member]            
Derivative [Line Items]            
Derivative liabilities 8.0     8.0   9.5
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     (0.2)   (0.5)  
Corporate [Member] | Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member]            
Derivative [Line Items]            
Derivative, Notional Amount $ 21.0     $ 21.0   183.0
Corporate [Member] | Foreign Exchange Contract [Member] | Cost of Sales [Member]            
Derivative [Line Items]            
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net     $ (2.4)   $ (3.3) $ (7.3)
[1] At June 30, 2014, the location of the Gain (Loss) Recognized in Income on Derivative for Foreign Exchange Contracts was Cost of goods sold and operating expenses.