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DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | ||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Sep. 30, 2014
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Sep. 30, 2013
|
Sep. 30, 2014
|
Sep. 30, 2013
|
Sep. 30, 2014
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
|
Sep. 30, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
|
Sep. 30, 2014
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
|
Sep. 30, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
|
Sep. 30, 2014
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Product Revenues [Member]
|
Sep. 30, 2013
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Product Revenues [Member]
|
Sep. 30, 2014
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Product Revenues [Member]
|
Sep. 30, 2013
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Product Revenues [Member]
|
Sep. 30, 2014
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
|
Dec. 31, 2013
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
|
Sep. 30, 2014
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
|
Sep. 30, 2014
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Cost of Sales [Member]
|
Sep. 30, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Cost of Sales [Member]
|
Sep. 30, 2014
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Cost of Sales [Member]
|
Sep. 30, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Cost of Sales [Member]
|
Sep. 30, 2014
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
|
Dec. 31, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
|
Sep. 30, 2014
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
|
Sep. 30, 2014
Interest Rate Swap [Member]
Other Nonoperating Income (Expense) [Member]
|
Sep. 30, 2013
Interest Rate Swap [Member]
Other Nonoperating Income (Expense) [Member]
|
Sep. 30, 2014
Interest Rate Swap [Member]
Other Nonoperating Income (Expense) [Member]
|
Sep. 30, 2013
Interest Rate Swap [Member]
Other Nonoperating Income (Expense) [Member]
|
Jun. 30, 2014
Interest Rate Swap [Member]
Designated as Hedging Instrument [Member]
|
Sep. 30, 2014
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member]
Not Designated as Hedging Instrument [Member]
|
Dec. 31, 2013
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member]
Not Designated as Hedging Instrument [Member]
|
Sep. 30, 2014
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member]
Not Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
|
Sep. 30, 2014
Foreign Exchange Contract [Member]
Cost of Sales [Member]
|
Sep. 30, 2013
Foreign Exchange Contract [Member]
Cost of Sales [Member]
|
Sep. 30, 2014
Foreign Exchange Contract [Member]
Cost of Sales [Member]
|
Sep. 30, 2013
Foreign Exchange Contract [Member]
Cost of Sales [Member]
|
Sep. 30, 2014
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
|
Sep. 30, 2013
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
|
Sep. 30, 2014
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
|
Sep. 30, 2013
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
|
Sep. 30, 2014
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Derivative Financial Instruments, Assets [Member]
|
Dec. 31, 2013
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Derivative Financial Instruments, Assets [Member]
|
Sep. 30, 2014
Provisional Pricing Arrangements [Member]
Product Revenues [Member]
|
Sep. 30, 2013
Provisional Pricing Arrangements [Member]
Product Revenues [Member]
|
Sep. 30, 2014
Provisional Pricing Arrangements [Member]
Product Revenues [Member]
|
Sep. 30, 2013
Provisional Pricing Arrangements [Member]
Product Revenues [Member]
|
Sep. 30, 2014
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]
|
Sep. 30, 2013
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]
|
Sep. 30, 2014
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]
|
Sep. 30, 2013
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]
|
Sep. 30, 2014
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
Derivative Financial Instruments, Assets [Member]
|
Dec. 31, 2013
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
Derivative Financial Instruments, Assets [Member]
|
Sep. 30, 2014
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
Derivative Financial Instruments, Liabilities [Member]
|
Dec. 31, 2013
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
Derivative Financial Instruments, Liabilities [Member]
|
|
| Derivative [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||
| Derivative, Notional Amount | $ 285.0 | $ 323.0 | $ 257.4 | $ 285.9 | $ 250.0 | $ 0 | $ 74.8 | |||||||||||||||||||||||||||||||||||||||||||||
| Gain (Loss) on Fair Value Hedge Ineffectiveness, Net | 0.1 | 0.1 | 0.3 | 0.1 | ||||||||||||||||||||||||||||||||||||||||||||||||
| Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net | 59.5 | 75.5 | 98.0 | 103.9 | 0 | 0 | (3.3) | 0 | (3.1) | 24.3 | (23.3) | (6.8) | ||||||||||||||||||||||||||||||||||||||||
| Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | 0.6 | (16.2) | (18.8) | (12.0) | 0 | 0 | (0.5) | 0 | 1.6 | (8.9) | (11.2) | (4.5) | (1.0) | (7.3) | (7.1) | (7.5) | ||||||||||||||||||||||||||||||||||||
| Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts | (7.4) | (5.0) | 0 | |||||||||||||||||||||||||||||||||||||||||||||||||
| Amount of gain/(loss) recognized in income on derivative | 62.6 | 53.9 | 124.6 | 113.4 | (3.1) | 24.3 | (23.3) | (6.8) | ||||||||||||||||||||||||||||||||||||||||||||
| Derivative assets | 54.5 | 55.8 | 0 | 3.1 | ||||||||||||||||||||||||||||||||||||||||||||||||
| Derivative liabilities | $ 23.3 | $ 10.3 | ||||||||||||||||||||||||||||||||||||||||||||||||||