SEGMENT REPORTING (Schedule Of Segment Reporting Information, By Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	100.00%		100.00%		100.00%		100.00%
Revenues from product sales and services	$ 1,546.6		$ 1,544.9		$ 4,175.6		$ 4,336.8
Sales Margin	348.7		198.3		854.8		933.6
Other operating expense	(124.7)		(122.0)		(200.5)		(272.3)
Other expense	(45.9)		(43.9)		(137.4)		(134.7)
Income from Continuing Operations before income taxes and equity (loss) from ventures	178.1		32.4		516.9		526.6
Depreciation, depletion and amortization	153.1		132.9		438.0		382.3
Capital Additions	211.3	[1]	354.5	[1]	625.1	[1]	974.0	[1]
U.S. Iron Ore [Member]
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	51.00%		52.00%		45.00%		45.00%
Revenues from product sales and services	782.4		796.0		1,894.2		1,942.7
Sales Margin	273.5		255.9		647.1		708.9
Depreciation, depletion and amortization	27.3		24.9		82.3		71.9
Capital Additions	15.2	[1]	19.6	[1]	39.1	[1]	82.5	[1]
Eastern Canadian Iron Ore [Member]
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	18.00%		16.00%		18.00%		18.00%
Revenues from product sales and services	284.2		253.1		743.4		777.8
Sales Margin	(22.0)		(40.5)		(52.3)		(43.0)
Depreciation, depletion and amortization	46.8		41.7		130.3		118.2
Capital Additions	181.5	[1]	285.5	[1]	535.3	[1]	593.4	[1]
Asia Pacific Iron Ore [Member]
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	20.00%		16.00%		22.00%		22.00%
Revenues from product sales and services	301.7		254.2		899.5		975.3
Sales Margin	99.0		(15.8)		255.3		256.1
Depreciation, depletion and amortization	38.0		40.2		116.1		110.0
Capital Additions	2.0	[1]	5.8	[1]	8.6	[1]	132.0	[1]
North American Coal [Member]
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	11.00%		16.00%		15.00%		15.00%
Revenues from product sales and services	178.3		241.8		638.5		640.9
Sales Margin	(1.8)		(1.3)		6.6		3.8
Depreciation, depletion and amortization	38.8		25.1		99.7		69.5
Capital Additions	10.4	[1]	33.3	[1]	37.2	[1]	105.1	[1]
All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	0.00%		0.00%		0.00%		0.00%
Revenues from product sales and services	0		(0.2)		0		0.1
Sales Margin	0		0		(1.9)		7.8
Depreciation, depletion and amortization	2.2		1.0		9.6		12.7
Capital Additions	$ 2.2	[1]	$ 10.3	[1]	$ 4.9	[1]	$ 61.0	[1]

[1] Includes capital lease additions and non-cash accruals. Refer to NOTE 20 - CASH FLOW INFORMATION.