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Business Summary And Significant Accounting Policies (Narrative) (Details)
In Millions, except Per Share data, unless otherwise specified |
12 Months Ended | 3 Months Ended | 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, 2011
USD ($)
MT
|
Dec. 31, 2010
USD ($)
|
Dec. 31, 2009
USD ($)
|
Dec. 31, 2011
SMM [Member]
USD ($)
|
Dec. 31, 2010
SMM [Member]
USD ($)
|
Dec. 31, 2009
SMM [Member]
USD ($)
|
Dec. 31, 2011
Arcelor Mittal [Member]
|
Dec. 31, 2011
CLCC [Member]
USD ($)
|
Dec. 31, 2011
Consolidated Thompson [Member]
|
May 13, 2011
Consolidated Thompson [Member]
CAD
|
Dec. 31, 2011
Amapa [Member]
USD ($)
|
Dec. 31, 2010
Amapa [Member]
USD ($)
|
Dec. 31, 2009
Amapa [Member]
USD ($)
|
Dec. 31, 2011
AusQuest [Member]
USD ($)
|
Jun. 30, 2011
AusQuest [Member]
USD ($)
|
Dec. 31, 2011
Hibbing And Cockatoo [Member]
USD ($)
|
Dec. 31, 2011
Sonoma [Member]
|
Dec. 31, 2011
Sonoma [Member]
CAWO [Member]
|
Dec. 31, 2011
Sonoma [Member]
Mining Assets [Member]
|
Dec. 31, 2011
Sonoma [Member]
Non- Mining Assets [Member]
|
Dec. 31, 2011
RenewaFUEL [Member]
USD ($)
|
Dec. 31, 2010
RenewaFUEL [Member]
USD ($)
|
Dec. 31, 2009
RenewaFUEL [Member]
USD ($)
|
Feb. 28, 2010
Wabush [Member]
|
Feb. 01, 2010
Wabush [Member]
|
Dec. 31, 2011
CAC [Member]
CAWO [Member]
|
Dec. 31, 2011
North American Iron Ore [Member]
|
Dec. 31, 2011
Metallurgical Coal Mines [Member]
|
Dec. 31, 2011
Thermal Coal Mines [Member]
|
Dec. 31, 2011
Eastern Canadian Iron Ore [Member]
USD ($)
|
Dec. 31, 2010
Eastern Canadian Iron Ore [Member]
USD ($)
|
Dec. 31, 2011
Eastern Canadian Iron Ore [Member]
Consolidated Thompson [Member]
|
Dec. 31, 2011
Eastern Canadian Iron Ore [Member]
WISCO [Member]
|
Dec. 31, 2011
U.S. Iron Ore [Member]
USD ($)
|
Dec. 31, 2010
U.S. Iron Ore [Member]
USD ($)
|
Dec. 31, 2009
U.S. Iron Ore [Member]
USD ($)
|
Dec. 31, 2011
North American Coal [Member]
USD ($)
|
Dec. 31, 2010
North American Coal [Member]
USD ($)
|
Dec. 31, 2009
North American Coal [Member]
USD ($)
|
Dec. 31, 2011
Asia Pacific Iron Ore [Member]
USD ($)
|
Dec. 31, 2010
Asia Pacific Iron Ore [Member]
USD ($)
|
|
| Purchase price of acquiree, in dollars per share | 17.25 | ||||||||||||||||||||||||||||||||||||||||
| Number of mines | 2 | 5 | 1 | 2 | 5 | 2 | |||||||||||||||||||||||||||||||||||
| Loss from discontinued operations | $ 18.5 | $ 3.1 | $ 3.4 | ||||||||||||||||||||||||||||||||||||||
| Discontinued Operation, Tax Effect of Discontinued Operation | 9.2 | ||||||||||||||||||||||||||||||||||||||||
| Tax benefits to write the assets down to fair value | 8.0 | ||||||||||||||||||||||||||||||||||||||||
| Tax benefits | 420.1 | 293.5 | 22.5 | 1.5 | 1.7 | ||||||||||||||||||||||||||||||||||||
| Excess of current cost over LIFO cost of iron ore inventories | 21.9 | 2.5 | 117.1 | 112.4 | |||||||||||||||||||||||||||||||||||||
| Iron ore concentrate inventory | 49.1 | ||||||||||||||||||||||||||||||||||||||||
| Deferred Revenue from prior year to be recongized in future years | 15.1 | ||||||||||||||||||||||||||||||||||||||||
| Decrease in cost of goods sold and operations expense | (4,105.7) | (3,155.6) | (2,030.3) | (15.2) | 4.6 | ||||||||||||||||||||||||||||||||||||
| Tons of finished goods stored at ports on the lower Great Lakes to service customers | 1,200,000 | 800,000 | |||||||||||||||||||||||||||||||||||||||
| Depreciation expense | 237.8 | 165.4 | 120.6 | ||||||||||||||||||||||||||||||||||||||
| Depletion expense | 159.7 | 95.5 | 68.1 | ||||||||||||||||||||||||||||||||||||||
| Increase in inventory of finished goods | 47.1 | ||||||||||||||||||||||||||||||||||||||||
| Product Inventory Balance | 291.3 | 198.0 | 96.2 | 43.5 | 100.2 | 101.1 | 19.7 | 16.1 | 57.2 | 34.7 | |||||||||||||||||||||||||||||||
| Inventory Write-down | 6.6 | 26.1 | |||||||||||||||||||||||||||||||||||||||
| Business Acquisition, Percentage of Voting Interests Acquired | 45.00% | ||||||||||||||||||||||||||||||||||||||||
| Description of venture operations | SMM is the appointed operator of the mine assets, non-mine assets and the washplant. | ||||||||||||||||||||||||||||||||||||||||
| Equity Method Investment, Quoted Market Value | 3.7 | ||||||||||||||||||||||||||||||||||||||||
| Investment Owned, Balance, Shares | 68.3 | ||||||||||||||||||||||||||||||||||||||||
| Portion of Environmental Exit Costs, Reasonably Possible Additional Losses, Estimate | 20.0 | ||||||||||||||||||||||||||||||||||||||||
| Percent ownership interest | 30.00% | 30.00% | 50.00% | 26.80% | |||||||||||||||||||||||||||||||||||||
| Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions | 100.00% | ||||||||||||||||||||||||||||||||||||||||
| Percent ownership interest | 100.00% | 25.00% | |||||||||||||||||||||||||||||||||||||||
| Percent ownership interest in wholly-owned subsidiary | 100.00% | 100.00% | 100.00% | ||||||||||||||||||||||||||||||||||||||
| Percent economic interest in venture | 45.00% | ||||||||||||||||||||||||||||||||||||||||
| Percent ownership interest in venture | 79.00% | 21.00% | 8.33% | 45.00% | |||||||||||||||||||||||||||||||||||||
| Percent interest owned | 73.20% | ||||||||||||||||||||||||||||||||||||||||
| Percent interest acquired | 79.00% | ||||||||||||||||||||||||||||||||||||||||
| Payments to acquire interest in venture | 3.1 | 3.3 | 8.6 | ||||||||||||||||||||||||||||||||||||||
| Percent of Sonoma coal production to coal washing services | 40.00% | ||||||||||||||||||||||||||||||||||||||||
| Total investment | 504.8 | 509.0 | 147.9 | ||||||||||||||||||||||||||||||||||||||
| Goodwill | 1,152.1 | 196.5 | 74.6 | ||||||||||||||||||||||||||||||||||||||
| Goodwill, Impairment Loss | 27.8 | 27.8 | |||||||||||||||||||||||||||||||||||||||
| EQUITY INCOME (LOSS) FROM VENTURES | 9.7 | 13.5 | (65.5) | 32.4 | 17.2 | (62.2) | |||||||||||||||||||||||||||||||||||
| Impairment charge | 19.1 | 16.0 | |||||||||||||||||||||||||||||||||||||||
| Reimbursement for freight charges paid on behalf of customers | 224.3 | 223.4 | 93.7 | 18.3 | 41.9 | 32.1 | |||||||||||||||||||||||||||||||||||
| Deferred revenue | 15.8 | 155.3 | |||||||||||||||||||||||||||||||||||||||
| Under take-or-pay contracts, customers purchased tons of pellets stored in upper lakes stockpiles | 200,000 | 2,400,000 | |||||||||||||||||||||||||||||||||||||||
| Tons of pellets shipped deferred from previous year | 2,400,000 | ||||||||||||||||||||||||||||||||||||||||
| Remaining Quantity Of Goods Deferred Revenue Revenue Recognized, Tons | 100,000 | ||||||||||||||||||||||||||||||||||||||||
| Estimated useful life, Repairs and maintenance | five | ||||||||||||||||||||||||||||||||||||||||
| Changes in deferred revenue and below-market sales contracts | $ 91.7 | $ 58.1 | |||||||||||||||||||||||||||||||||||||||