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DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | |||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Jun. 30, 2013
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Jun. 30, 2013
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Dec. 31, 2012
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Jun. 30, 2013
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
|
Dec. 31, 2012
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
|
Jun. 30, 2013
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
|
Jun. 30, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
|
Dec. 31, 2012
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
|
Jun. 30, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
|
Jun. 30, 2013
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
|
Jun. 30, 2012
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
|
Jun. 30, 2013
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
|
Jun. 30, 2012
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
|
Jun. 30, 2013
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Derivative Assets [Member]
|
Dec. 31, 2012
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Derivative Assets [Member]
|
Jun. 30, 2013
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
|
Jun. 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]
|
Jun. 30, 2012
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]
|
Jun. 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]
|
Jun. 30, 2012
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]
|
Jun. 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]
Derivative Assets [Member]
|
Jun. 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]
Derivative Liabilities [Member]
|
Dec. 31, 2012
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Derivative Assets [Member]
|
Dec. 31, 2012
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Derivative Liabilities [Member]
|
Jun. 30, 2012
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore [Member]
Product Revenues [Member]
|
Jun. 30, 2012
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore [Member]
Product Revenues [Member]
|
|
| Derivative [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Notional amounts of outstanding exchange rate contracts | Ìý | Ìý | Ìý | $ 358.0 | $ 400.0 | Ìý | $ 611.7 | $ 630.4 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts | Ìý | Ìý | Ìý | Ìý | Ìý | (24.7) | Ìý | Ìý | (15.6) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Amount of gain/(loss) recognized in income on derivative | (2.2) | (4.2) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 35.4 | 42.6 | 59.5 | 82.0 | Ìý | Ìý | 0 | (28.2) | (5.2) | (31.1) | (2.2) | Ìý | Ìý | Ìý | Ìý | 96.1 | 96.1 |
| Derivative assets | 45.1 | 45.1 | 78.6 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 44.2 | 58.9 | Ìý | Ìý | Ìý | Ìý | Ìý | 0.9 | Ìý | 3.5 | Ìý | Ìý | Ìý |
| Derivative liabilities | $ 88.6 | $ 88.6 | $ 13.2 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 32.0 | Ìý | $ 11.3 | Ìý | Ìý |