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Derivative Instruments And Hedging Activities (Narrative) (Detail)
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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, 2012
USD ($)
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Sep. 30, 2011
USD ($)
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Sep. 30, 2012
USD ($)
|
Sep. 30, 2011
USD ($)
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Dec. 31, 2011
USD ($)
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Sep. 30, 2012
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
USD ($)
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Sep. 30, 2012
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
USD ($)
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Sep. 30, 2012
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
USD ($)
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Dec. 31, 2011
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
USD ($)
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Sep. 30, 2011
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
aud_per_usd
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Sep. 30, 2012
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
USD ($)
|
Dec. 31, 2011
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
USD ($)
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Sep. 30, 2012
Foreign Exchange Contract [Member]
USD ($)
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Sep. 30, 2012
Foreign Exchange Contract [Member]
USD ($)
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Sep. 30, 2011
Foreign Exchange Contract [Member]
Consolidated Thompson [Member]
USD ($)
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Jan. 11, 2011
Foreign Exchange Contract [Member]
Consolidated Thompson [Member]
CAD
|
Sep. 30, 2012
Customer Contracts [Member]
USD ($)
|
Dec. 31, 2011
Customer Contracts [Member]
USD ($)
|
Sep. 30, 2012
Customer Contracts [Member]
Product Revenue [Member]
USD ($)
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Sep. 30, 2011
Customer Contracts [Member]
Product Revenue [Member]
USD ($)
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Sep. 30, 2012
Customer Contracts [Member]
Product Revenue [Member]
USD ($)
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Sep. 30, 2011
Customer Contracts [Member]
Product Revenue [Member]
USD ($)
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Sep. 30, 2012
Provisional Pricing Arrangements [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Product Revenue [Member]
USD ($)
|
Sep. 30, 2011
Provisional Pricing Arrangements [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
Product Revenue [Member]
USD ($)
|
Sep. 30, 2012
Sonoma [Member]
Asia Pacific Coal [Member]
AUD
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Dec. 31, 2011
Derivative Financial Instruments, Assets [Member]
Provisional Pricing Arrangements [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
USD ($)
|
Dec. 31, 2011
Derivative Financial Instruments, Liabilities [Member]
Provisional Pricing Arrangements [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
USD ($)
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Dec. 31, 2011
Accounts Receivable [Member]
Provisional Pricing Arrangements [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
USD ($)
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Sep. 30, 2012
Not Designated as Hedging Instrument [Member]
USD ($)
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Dec. 31, 2011
Not Designated as Hedging Instrument [Member]
USD ($)
|
Sep. 30, 2012
Not Designated as Hedging Instrument [Member]
Foreign Exchange Contract [Member]
USD ($)
|
Dec. 31, 2011
Not Designated as Hedging Instrument [Member]
Foreign Exchange Contract [Member]
USD ($)
|
Sep. 30, 2012
Not Designated as Hedging Instrument [Member]
Customer Contracts [Member]
USD ($)
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Dec. 31, 2011
Not Designated as Hedging Instrument [Member]
Customer Contracts [Member]
USD ($)
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Sep. 30, 2012
Not Designated as Hedging Instrument [Member]
Provisional Pricing Arrangements [Member]
USD ($)
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Dec. 31, 2011
Not Designated as Hedging Instrument [Member]
Provisional Pricing Arrangements [Member]
USD ($)
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Sep. 30, 2012
Not Designated as Hedging Instrument [Member]
Liabilities Of Assets Held For Sale [Member]
Foreign Exchange Contract [Member]
USD ($)
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Dec. 31, 2011
Not Designated as Hedging Instrument [Member]
Liabilities Of Assets Held For Sale [Member]
Foreign Exchange Contract [Member]
USD ($)
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| Derivative liability, fair value | $ 13,000,000 | $ 13,000,000 | $ 23,000,000 | $ 11,700,000 | $ 19,500,000 | |||||||||||||||||||||||||||||||||
| Notional amounts of outstanding exchange rate contracts | 420,000,000 | 400,000,000 | 645,700,000 | 0 | ||||||||||||||||||||||||||||||||||
| Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts | 8,700,000 | 6,200,000 | ||||||||||||||||||||||||||||||||||||
| Ownership interest, percent | 45.00% | |||||||||||||||||||||||||||||||||||||
| Proceeds from Divestiture of Interest in Joint Venture | 141,000,000 | |||||||||||||||||||||||||||||||||||||
| Amount of gain/(loss) recognized in income on derivative | 0 | (6,200,000) | 300,000 | 100,500,000 | 1,100,000 | 1,100,000 | 93,100,000 | |||||||||||||||||||||||||||||||
| Foreign Currency Spot Rate | 1.04 | |||||||||||||||||||||||||||||||||||||
| Assets Held-for-sale, Current | 156,600,000 | 156,600,000 | 159,900,000 | 1,100,000 | 1,100,000 | |||||||||||||||||||||||||||||||||
| Notional amount of foreign currency derivative instruments not designated as hedging instruments | 4,700,000,000 | |||||||||||||||||||||||||||||||||||||
| Amount of gain/(loss) recognized in income on derivative | (10,300,000) | (10,300,000) | 49,800,000 | 53,800,000 | 131,800,000 | 124,900,000 | 623,500,000 | 193,000,000 | ||||||||||||||||||||||||||||||
| Derivative assets | 78,300,000 | 78,300,000 | 82,100,000 | 1,400,000 | 1,400,000 | 54,500,000 | 72,900,000 | 1,200,000 | ||||||||||||||||||||||||||||||
| Derivative liabilities | 11,700,000 | 11,700,000 | 19,500,000 | |||||||||||||||||||||||||||||||||||
| Accounts receivable | $ 285,900,000 | $ 285,900,000 | $ 287,900,000 | $ 83,800,000 | ||||||||||||||||||||||||||||||||||