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DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details) (USD $)
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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 | 9 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | |||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
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Dec. 31, 2012
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
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Dec. 31, 2011
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member]
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Dec. 31, 2012
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member]
Not Designated as Hedging Instrument [Member]
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Dec. 31, 2013
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member]
Not Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
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Dec. 31, 2013
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
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Dec. 31, 2012
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
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Dec. 31, 2011
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
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Dec. 31, 2013
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Product Revenues [Member]
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Dec. 31, 2012
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Product Revenues [Member]
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Dec. 31, 2011
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Product Revenues [Member]
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Dec. 31, 2013
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
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Dec. 31, 2012
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
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Dec. 31, 2013
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
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Dec. 31, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
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Dec. 31, 2012
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
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Dec. 31, 2011
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
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Dec. 31, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
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Dec. 31, 2012
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
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Dec. 31, 2013
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
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Dec. 31, 2013
Interest Rate Swap [Member]
Other Nonoperating Income Expense [Member]
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Dec. 31, 2013
Interest Rate Swap [Member]
Designated as Hedging Instrument [Member]
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Dec. 31, 2013
Treasury Lock [Member]
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Dec. 31, 2012
Treasury Lock [Member]
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Dec. 31, 2011
Treasury Lock [Member]
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Dec. 31, 2013
Treasury Lock [Member]
Changes in Fair Value of Foreign Currency Contracts, Net [Member]
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Dec. 31, 2012
Treasury Lock [Member]
Changes in Fair Value of Foreign Currency Contracts, Net [Member]
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Dec. 31, 2011
Treasury Lock [Member]
Changes in Fair Value of Foreign Currency Contracts, Net [Member]
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Dec. 31, 2011
Treasury Lock [Member]
Designated as Hedging Instrument [Member]
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Dec. 31, 2012
Treasury Lock [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
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Dec. 31, 2013
Treasury Lock [Member]
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
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Dec. 31, 2013
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
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Dec. 31, 2012
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
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Dec. 31, 2011
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Product Revenues [Member]
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Dec. 31, 2013
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Derivative Financial Instruments, Assets [Member]
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Dec. 31, 2012
Customer Supply Agreement [Member]
Not Designated as Hedging Instrument [Member]
Derivative Financial Instruments, Assets [Member]
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Sep. 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]
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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]
Product Revenues [Member]
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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]
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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]
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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]
Product Revenues [Member]
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Dec. 31, 2012
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Derivative Financial Instruments, Assets [Member]
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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 Financial Instruments, Assets [Member]
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Dec. 31, 2012
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Derivative Financial Instruments, Liabilities [Member]
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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 Financial Instruments, Liabilities [Member]
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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]
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Dec. 31, 2011
Provisional Pricing Arrangements [Member]
Not Designated as Hedging Instrument [Member]
U.S. Iron Ore [Member]
Product Revenues [Member]
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Dec. 31, 2013
$500 Million 3.95% 2018 Senior Notes [Member]
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Dec. 31, 2012
$500 Million 3.95% 2018 Senior Notes [Member]
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| Derivative [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||
| Gain (Loss) on Fair Value Hedge Ineffectiveness, Net | $ 100,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Debt Instrument, Face Amount | 4,814,800,000 | 5,497,100,000 | 500,000,000.0 | 500,000,000.0 | ||||||||||||||||||||||||||||||||||||||||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net | (51,700,000) | 25,600,000 | 1,800,000 | (4,100,000) | 0 | 0 | (34,700,000) | 20,200,000 | 1,800,000 | (12,900,000) | 6,700,000 | (1,300,000) | (1,300,000) | |||||||||||||||||||||||||||||||||||||||
| Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net | (22,100,000) | 18,100,000 | 3,300,000 | (1,900,000) | 0 | 0 | (11,900,000) | 14,800,000 | 2,600,000 | (100,000) | 0 | 0 | ||||||||||||||||||||||||||||||||||||||||
| Derivative, Notional Amount | 74,800,000 | 323,000,000 | 400,000,000 | 285,900,000 | 630,400,000 | 250,000,000 | 200,000,000 | |||||||||||||||||||||||||||||||||||||||||||||
| Debt, length of maturity, years | 5 years | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts | (500,000) | (15,000,000) | 2,900,000 | (100,000) | ||||||||||||||||||||||||||||||||||||||||||||||||
| Amount of gain/(loss) recognized in income on derivative | 149,200,000 | 171,400,000 | 178,000,000 | (7,800,000) | (7,200,000) | 809,100,000 | 309,400,000 | |||||||||||||||||||||||||||||||||||||||||||||
| Derivative assets | 55,800,000 | 58,900,000 | 3,100,000 | 3,500,000 | 1,200,000 | |||||||||||||||||||||||||||||||||||||||||||||||
| Derivative liabilities | 10,300,000 | 11,300,000 | 19,500,000 | |||||||||||||||||||||||||||||||||||||||||||||||||
| Accounts receivable, net | $ 270,000,000 | $ 329,000,000 | $ 83,800,000 | |||||||||||||||||||||||||||||||||||||||||||||||||