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)