INTANGIBLE ASSETS (Schedule of Intangible Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	$ 418.7	$ 426.3
Accumulated Amortization	(160.2)	(146.3)
Intangible Assets, Net	258.5	280.0
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	94.6	102.2
Accumulated Amortization	(65.8)	(64.5)
Intangible Assets, Net	28.8	37.7
Natural gas supply opportunities [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	324.1	324.1
Accumulated Amortization	(94.4)	(81.8)
Intangible Assets, Net	$ 229.7	$ 242.3
Minimum [Member] | Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life (in years)	3 years
Minimum [Member] | Natural gas supply opportunities [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life (in years)	15 years
Maximum [Member] | Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life (in years)	25 years
Maximum [Member] | Natural gas supply opportunities [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life (in years)	30 years