PROPERTY, PLANT AND EQUIPMENT (Value Of Each Of The Major Classes Of Consolidated Depreciable Assets) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 13,525.8	$ 13,044.7
Allowance for depreciation and depletion	(2,171.0)	(1,837.4)
Property, plant and equipment, net	11,354.8	11,207.3
Land Rights And Mineral Rights [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,826.5	7,920.8
Office And Information Technology [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	119.3	92.4
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	214.0	162.0
Mining Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,554.7	1,290.7
Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,172.8	1,937.4
Railroad Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	222.3	240.8
Electric Power Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	82.9	58.7
Port Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	103.8	114.3
Capitalized Interest Charges [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	25.5	20.8
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	63.0	43.9
Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	91.8	39.0
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,049.2	$ 1,123.9