Annual report pursuant to Section 13 and 15(d)

DISCONTINUED OPERATIONS Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis - North American Coal (Details)

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DISCONTINUED OPERATIONS Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis - North American Coal (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items]          
Tangible Asset Impairment Charges     $ 0 $ 0 $ 537,800,000
North American Coal [Member]          
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items]          
Property, Plant, and Equipment, Fair Value Disclosure   $ 20,400,000      
Tangible Asset Impairment Charges   73,400,000      
Assets, Fair Value Disclosure, Nonrecurring   20,400,000      
Impairment Charges $ 73,400,000        
Fair Value, Inputs, Level 1 [Member] | North American Coal [Member]          
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items]          
Property, Plant, and Equipment, Fair Value Disclosure   0      
Assets, Fair Value Disclosure, Nonrecurring   0      
Fair Value, Inputs, Level 2 [Member] | North American Coal [Member]          
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items]          
Property, Plant, and Equipment, Fair Value Disclosure   0      
Assets, Fair Value Disclosure, Nonrecurring   0      
Fair Value, Inputs, Level 3 [Member] | North American Coal [Member]          
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items]          
Property, Plant, and Equipment, Fair Value Disclosure   20,400,000      
Assets, Fair Value Disclosure, Nonrecurring   $ 20,400,000