Statements Of Consolidated Changes In Equity (USD $) In Millions, except Share data, unless otherwise specified	Common Shares [Member]	Capital In Excess of Par Value of Shares [Member]	Retained Earnings [Member]	Common Shares in Treasury [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non- Controlling Interest [Member]	Total
Beginning Balance at Dec. 31, 2008	$ 16.8	$ 442.2	$ 1,799.9	$ (113.8)	$ (394.6)	$ 3.3	$ 1,753.8
Beginning Balance (in shares) at Dec. 31, 2008	113,500,000
Comprehensive income
Net income			205.1				205.1
Other comprehensive income (loss), net of tax
Pension and OPEB liability					24.2	(2.4)	21.8
Unrealized net gain on marketable securities					29.5		29.5
Unrealized net gain on foreign currency translation					231.7		231.7
Unrealized gain on interest rate swap					1.7		1.7
Reclassification of net gains on derivative financial instruments into net income					(15.1)		(15.1)
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS						(2.4)	474.7
Purchase of subsidiary shares from noncontrolling interest						0.1	0.1
Undistributed losses to noncontrolling interest						(7.5)	(7.5)
Capital contribution by noncontrolling interest to subsidiary						0.7	0.7
Equity Offering (in shares)	17,300,000
Equity Offering (value)		254.5		92.8			347.3
Purchase of additional noncontrolling interest		(5.4)					(5.4)
Stock and other incentive plans (in shares)	200,000
Stock and other incentive plans		4.1		0.9			5.0
Conversion of preferred stock				0.2			0.2
Common stock dividends			(31.9)				(31.9)
Ending Balance at Dec. 31, 2009	16.8	695.4	1,973.1	(19.9)	(122.6)	(5.8)	2,537.0
Ending Balance (in shares) at Dec. 31, 2009	131,000,000
Comprehensive income
Net income			1,019.9				1,019.9
Other comprehensive income (loss), net of tax
Pension and OPEB liability					14.0	0.8	14.8
Unrealized net gain on marketable securities					4.2		4.2
Unrealized net gain on foreign currency translation					151.6		151.6
Reclassification of net gains on derivative financial instruments into net income					(3.2)		(3.2)
Unrealized gain on derivative instruments					1.9		1.9
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS						0.8	1,189.2
Purchase of subsidiary shares from noncontrolling interest						(0.5)	(0.5)
Undistributed losses to noncontrolling interest						(4.7)	(4.7)
Capital contribution by noncontrolling interest to subsidiary						3.0	3.0
Purchase of additional noncontrolling interest		(1.6)					(1.6)
Acquisition of controlling interest (in shares)	4,200,000
Acquisition of controlling interest	0.5	172.6					173.1
Stock and other incentive plans (in shares)	300,000
Stock and other incentive plans		19.4		(7.3)			12.1
Common stock dividends			(68.9)				(68.9)
Other		10.5		(10.5)
Ending Balance at Dec. 31, 2010	17.3	896.3	2,924.1	(37.7)	45.9	(7.2)	3,838.7
Ending Balance (in shares) at Dec. 31, 2010	135,500,000						135,456,999
Comprehensive income
Net income			1,619.1			193.5	1,812.6
Other comprehensive income (loss), net of tax
Pension and OPEB liability					(103.8)	(17.6)	(121.4)
Unrealized net gain on marketable securities					(31.0)		(31.0)
Unrealized net gain on foreign currency translation					(2.2)		(2.2)
Reclassification of net gains on derivative financial instruments into net income					(3.3)		(3.3)
Unrealized gain on derivative instruments					1.8		1.8
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS						175.9	1,656.5
Purchase of subsidiary shares from noncontrolling interest						4.5	4.5
Capital contribution by noncontrolling interest to subsidiary		0.2				6.1	6.3
Share buyback (in shares)	(4,000,000)
Share buyback				(289.8)			(289.8)
Equity Offering (in shares)	10,300,000
Equity Offering (value)	1.2	852.5					853.7
Acquisition of controlling interest						1,075.4	1,075.4
Stock and other incentive plans (in shares)	200,000
Stock and other incentive plans		21.8		(8.5)			13.3
Common stock dividends			(118.9)				(118.9)
Ending Balance at Dec. 31, 2011	$ 18.5	$ 1,770.8	$ 4,424.3	$ (336.0)	$ (92.6)	$ 1,254.7	$ 7,039.7
Ending Balance (in shares) at Dec. 31, 2011	142,000,000						142,021,718