BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)	3 Months Ended
	Mar. 31, 2013
Northshore [Member]
Related Party Transaction [Line Items]
Location	Minnesota
Ownership Interest	100.00%
Operation	Iron Ore
United Taconite [Member]
Related Party Transaction [Line Items]
Location	Minnesota
Ownership Interest	100.00%
Operation	Iron Ore
Wabush [Member]
Related Party Transaction [Line Items]
Location	Newfoundland and Labrador/Quebec, Canada
Ownership Interest	100.00%
Operation	Iron Ore
Bloom Lake [Member]
Related Party Transaction [Line Items]
Location	Quebec, Canada
Ownership Interest	75.00%
Operation	Iron Ore
Tilden [Member]
Related Party Transaction [Line Items]
Location	Michigan
Ownership Interest	85.00%
Operation	Iron Ore
Empire [Member]
Related Party Transaction [Line Items]
Location	Michigan
Ownership Interest	79.00%
Operation	Iron Ore
Koolyanobbing [Member]
Related Party Transaction [Line Items]
Location	Western Australia
Ownership Interest	100.00%
Operation	Iron Ore
Pinnacle [Member]
Related Party Transaction [Line Items]
Location	West Virginia
Ownership Interest	100.00%
Operation	Coal
Oak Grove [Member]
Related Party Transaction [Line Items]
Location	Alabama
Ownership Interest	100.00%
Operation	Coal
CLCC [Member]
Related Party Transaction [Line Items]
Location	West Virginia
Ownership Interest	100.00%
Operation	Coal