Quarterly report pursuant to Section 13 or 15(d)

Basis Of Presentation And Significant Accounting Policies (Impact Of The Prospective Adjustments On The Statements Of Unaudited Condensed Consolidated Operations ) (Details)

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Basis Of Presentation And Significant Accounting Policies (Impact Of The Prospective Adjustments On The Statements Of Unaudited Condensed Consolidated Operations ) (Details) (USD $)
In Millions, except Per Share data
3 Months Ended 9 Months Ended 3 Months Ended 6 Months Ended 9 Months Ended
Sep. 30, 2011
Sep. 30, 2010
Sep. 30, 2011
Sep. 30, 2010
Sep. 30, 2011
Immaterial Error [Member]
Jun. 30, 2011
Immaterial Error [Member]
Mar. 31, 2011
Immaterial Error [Member]
Jun. 30, 2011
Immaterial Error [Member]
Sep. 30, 2011
Immaterial Error [Member]
Product $ 2,124.4 $ 1,287.2 $ 4,962.4 $ 3,074.8 $ 54.1 $ 46.0 $ 54.1 $ 100.1 $ 54.1
Freight and venture partners' cost reimbursements 18.4 58.8 169.4 183.1 (46.0) (46.0)   (46.0) (46.0)
TOTAL REVENUES 2,142.8 1,346.0 5,131.8 3,257.9     54.1 54.1  
Cost of Goods Sold and Operating Expenses 1,279.5 868.8 2,936.9 2,215.3     (54.1) (54.1)  
Income from Continuing Operations 758.8 298.1 1,609.4 637.4 16.1 7.7 8.4 16.1 16.1
LESS: INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST 151.8   170.1     38.1 45.9 84.0 84.0
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 589.5 $ 297.4 $ 1,420.6 $ 635.4 $ 67.9 $ (30.4) $ (37.5) $ (67.9) $ 67.9
Earnings per Common Share Attributable to Cliffs Shareholders - Basic and Diluted         $ 0.47 $ (0.22) $ (0.28) $ (0.49)