Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments And Hedging Activities (Narrative) (Detail)

v2.4.0.6
Derivative Instruments And Hedging Activities (Narrative) (Detail)
3 Months Ended 9 Months Ended 3 Months Ended 9 Months Ended 3 Months Ended 9 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2012
USD ($)
Sep. 30, 2011
USD ($)
Sep. 30, 2012
USD ($)
Sep. 30, 2011
USD ($)
Dec. 31, 2011
USD ($)
Sep. 30, 2012
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
USD ($)
Sep. 30, 2012
U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member]
USD ($)
Sep. 30, 2012
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
USD ($)
Dec. 31, 2011
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
USD ($)
Sep. 30, 2011
Australian Dollar Foreign Exchange Contract Hedge Designation [Member]
aud_per_usd
Sep. 30, 2012
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
USD ($)
Dec. 31, 2011
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member]
USD ($)
Sep. 30, 2012
Foreign Exchange Contract [Member]
USD ($)
Sep. 30, 2012
Foreign Exchange Contract [Member]
USD ($)
Sep. 30, 2011
Foreign Exchange Contract [Member]
Consolidated Thompson [Member]
USD ($)
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 ($)
Sep. 30, 2011
Customer Contracts [Member]
Product Revenue [Member]
USD ($)
Sep. 30, 2012
Customer Contracts [Member]
Product Revenue [Member]
USD ($)
Sep. 30, 2011
Customer Contracts [Member]
Product Revenue [Member]
USD ($)
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
Dec. 31, 2011
Derivative Financial Instruments, Assets [Member]
Provisional Pricing Arrangements [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
USD ($)
Dec. 31, 2011
Derivative Financial Instruments, Liabilities [Member]
Provisional Pricing Arrangements [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
USD ($)
Dec. 31, 2011
Accounts Receivable [Member]
Provisional Pricing Arrangements [Member]
U.S. Iron Ore and Eastern Canadian Iron Ore [Member]
USD ($)
Sep. 30, 2012
Not Designated as Hedging Instrument [Member]
USD ($)
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 ($)
Sep. 30, 2012
Not Designated as Hedging Instrument [Member]
Customer Contracts [Member]
USD ($)
Dec. 31, 2011
Not Designated as Hedging Instrument [Member]
Customer Contracts [Member]
USD ($)
Sep. 30, 2012
Not Designated as Hedging Instrument [Member]
Provisional Pricing Arrangements [Member]
USD ($)
Dec. 31, 2011
Not Designated as Hedging Instrument [Member]
Provisional Pricing Arrangements [Member]
USD ($)
Sep. 30, 2012
Not Designated as Hedging Instrument [Member]
Liabilities Of Assets Held For Sale [Member]
Foreign Exchange Contract [Member]
USD ($)
Dec. 31, 2011
Not Designated as Hedging Instrument [Member]
Liabilities Of Assets Held For Sale [Member]
Foreign Exchange Contract [Member]
USD ($)
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