PROPERTY, PLANT AND EQUIPMENT (Value Of Each Of The Major Classes Of Consolidated Depreciable Assets) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 13,207.1	$ 13,044.7
Allowance for depreciation and depletion	(1,970.8)	(1,837.4)
Property, plant and equipment, net	11,236.3	11,207.3
Land Rights And Mineral Rights [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,922.8	7,920.8
Office And Information Technology [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	114.8	92.4
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	190.7	162.0
Mining Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,342.9	1,290.7
Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,081.9	1,937.4
Railroad Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	242.1	240.8
Electric Power Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	61.4	58.7
Port Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	114.7	114.3
Interest Capitalized During Construction [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20.8	20.8
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	48.7	43.9
Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	53.1	39.0
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,013.2	$ 1,123.9