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