PROPERTY, PLANT AND EQUIPMENT (Value Of Each Of The Major Classes Of Consolidated Depreciable Assets) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 4,174.5	$ 13,570.9
Accumulated Depreciation and Depletion, Property, Plant and Equipment	(966.6)	(2,417.5)
Property, plant and equipment, net	3,207.9	11,153.4
Land Rights And Mineral Rights [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,947.6	7,819.6
Office And Information Technology [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	80.7	125.7
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	88.9	255.2
Mining Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,399.5	1,819.3
Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	361.9	2,148.6
Electric Power Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	57.4	114.3
Port Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	27.6	99.4
Interest Capitalized During Construction [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	18.8	23.8
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	32.5	69.3
Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	65.5	104.4
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 94.1	$ 991.3