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DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details)
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12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | ||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2012
USD ($)
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Dec. 31, 2011
USD ($)
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Dec. 31, 2010
USD ($)
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Dec. 31, 2012
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
USD ($)
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Dec. 31, 2011
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
USD ($)
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Dec. 31, 2010
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
USD ($)
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Dec. 31, 2012
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
USD ($)
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Dec. 31, 2011
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
USD ($)
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Dec. 31, 2012
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
USD ($)
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Dec. 31, 2012
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
USD ($)
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Dec. 31, 2011
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
USD ($)
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Dec. 31, 2010
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
USD ($)
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Dec. 31, 2012
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
USD ($)
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Dec. 31, 2011
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
USD ($)
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Dec. 31, 2012
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
USD ($)
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Dec. 31, 2012
Treasury Lock [Member]
USD ($)
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Dec. 31, 2011
Treasury Lock [Member]
USD ($)
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Dec. 31, 2010
Treasury Lock [Member]
USD ($)
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Dec. 31, 2011
Treasury Lock [Member]
Designated as Hedging Instrument [Member]
USD ($)
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Dec. 31, 2012
Treasury Lock [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
USD ($)
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Dec. 31, 2012
Australian Dollar Foreign Exchange Contract Prior To De Designation [Member]
USD ($)
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Dec. 31, 2011
Australian Dollar Foreign Exchange Contract Prior To De Designation [Member]
USD ($)
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Dec. 31, 2010
Australian Dollar Foreign Exchange Contract Prior To De Designation [Member]
USD ($)
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Jan. 11, 2011
Foreign Exchange Contract [Member]
Not Designated as Hedging Instrument [Member]
Consolidated Thompson [Member]
CAD
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Dec. 31, 2011
Foreign Exchange Contract [Member]
Not Designated as Hedging Instrument [Member]
Consolidated Thompson [Member]
Changes in Fair Value of Foreign Currency Contracts, Net [Member]
USD ($)
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Nov. 13, 2012
Foreign Exchange Contract [Member]
Not Designated as Hedging Instrument [Member]
Sonoma [Member]
Asia Pacific Coal [Member]
aud_per_usd
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Dec. 31, 2012
Foreign Exchange Contract [Member]
Not Designated as Hedging Instrument [Member]
Sonoma [Member]
Asia Pacific Coal [Member]
Income (Loss) From Discontinued Operations [Member]
USD ($)
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Dec. 31, 2012
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
USD ($)
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Dec. 31, 2011
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
USD ($)
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Dec. 31, 2010
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
USD ($)
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Dec. 31, 2012
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Derivative Assets [Member]
USD ($)
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Dec. 31, 2011
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Derivative Assets [Member]
USD ($)
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Dec. 31, 2010
Provisional Pricing Arrangements [Member]
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
Product Revenues [Member]
USD ($)
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Dec. 31, 2011
Provisional Pricing Arrangements [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Product Revenues [Member]
USD ($)
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Dec. 31, 2011
Provisional Pricing Arrangements [Member]
U.S. Iron Ore [Member]
Product Revenues [Member]
USD ($)
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Dec. 31, 2012
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
Product Revenues [Member]
USD ($)
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Dec. 31, 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]
Derivative Assets [Member]
USD ($)
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Dec. 31, 2012
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
Other Current Liabilities [Member]
USD ($)
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Dec. 31, 2011
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Derivative Assets [Member]
USD ($)
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Dec. 31, 2011
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Other Current Liabilities [Member]
USD ($)
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Dec. 31, 2011
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Accounts Receivable [Member]
USD ($)
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Dec. 31, 2012
Senior Notes - $500 Million [Member]
USD ($)
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Dec. 31, 2011
Senior Notes - $500 Million [Member]
USD ($)
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Dec. 31, 2012
10-year Tranche - $500 million 4.80% Senior Notes due 2020 [Member]
USD ($)
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Dec. 31, 2011
10-year Tranche - $500 million 4.80% Senior Notes due 2020 [Member]
USD ($)
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Dec. 31, 2012
Sonoma [Member]
Asia Pacific Coal [Member]
AUD
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| Derivative [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||
| Notional amounts of outstanding exchange rate contracts | $ 400,000,000 | $ 400,000,000 | $ 630,400,000 | $ 0 | $ 200,000,000 | |||||||||||||||||||||||||||||||||||||||||
| Debt, length of maturity, years | 5 years | |||||||||||||||||||||||||||||||||||||||||||||
| Debt instrument, face amount | 5,497,100,000 | 5,447,000,000 | 500,000,000 | 500,000,000 | 500,000,000 | 500,000,000 | ||||||||||||||||||||||||||||||||||||||||
| Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | 25,600,000 | 1,800,000 | 1,900,000 | 20,200,000 | 1,800,000 | 1,900,000 | 6,700,000 | (1,300,000) | (1,300,000) | |||||||||||||||||||||||||||||||||||||
| Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts | 6,700,000 | 3,400,000 | 100,000 | |||||||||||||||||||||||||||||||||||||||||||
| Amount of gain/(loss) recognized in income on derivative | 171,400,000 | 178,000,000 | 120,200,000 | 960,700,000 | 809,100,000 | 309,400,000 | (7,800,000) | |||||||||||||||||||||||||||||||||||||||
| Foreign currency spot rate | 1.04 | |||||||||||||||||||||||||||||||||||||||||||||
| Ownership interest, percent | 45.00% | |||||||||||||||||||||||||||||||||||||||||||||
| Notional amount of forward contracts | 141,000,000 | |||||||||||||||||||||||||||||||||||||||||||||
| Amount of gain/(loss) recognized in income on derivative | (100,000) | 101,900,000 | 39,800,000 | 93,100,000 | (300,000) | |||||||||||||||||||||||||||||||||||||||||
| Notional amount of foreign currency derivative instruments not designated as hedging instruments | 4,700,000,000 | |||||||||||||||||||||||||||||||||||||||||||||
| Derivative assets | 78,600,000 | 82,100,000 | 58,900,000 | 72,900,000 | 3,500,000 | 1,200,000 | ||||||||||||||||||||||||||||||||||||||||
| Derivative liabilities | 11,300,000 | 19,500,000 | ||||||||||||||||||||||||||||||||||||||||||||
| Accounts receivable, net | $ 329,000,000 | $ 287,900,000 | $ 83,800,000 | |||||||||||||||||||||||||||||||||||||||||||