Quarterly Results Of Operations (Schedule Of Error Corrections And Prior Period Adjustments) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended			3 Months Ended		6 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jun. 30, 2011 Empire [Member]	Mar. 31, 2011 Empire [Member]	Jun. 30, 2011 Empire [Member]
Related Party Transaction [Line Items]
Product									$ 6,551.7	$ 4,416.8	$ 2,216.2	$ 46.0	$ 54.1	$ 100.1
Freight and venture partners' cost reimbursements									242.6	265.3	125.8	(46.0)		(46.0)
Revenues from product sales and services	1,662.5	2,142.8	1,805.8	1,183.2	1,424.1	1,346.0	1,184.3	727.7	6,794.3	4,682.1	2,342.0		54.1	54.1
Cost of Goods Sold and Operating Expenses									4,105.7	3,155.6	2,030.3		(54.1)	(54.1)
Income from Continuing Operations									2,348.6	1,270.2	236.1	7.7	8.4	16.1
LESS: NET INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST									193.5			38.1	45.9	84.0
Net Income Attributable to Cliffs Shareholders	$ 185.4	$ 601.2	$ 409.1	$ 423.4	$ 384.1	$ 297.6	$ 260.8	$ 77.4	$ 1,619.1	$ 1,019.9	$ 205.1	$ (30.4)	$ (37.5)	$ (67.9)
Earnings Per Share [Abstract]
Earnings Per Share, Basic and Diluted												$ (0.22)	$ (0.28)	$ (0.49)