DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES (Quantitative Information about Level 3 Fair Value Measurements) (Details) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) $ / bbl $ / MMBTU $ / gal		Dec. 31, 2014 USD ($) $ / bbl $ / MMBTU $ / gal $ / MWh
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets and liabilities accounted for at fair value on a recurring basis	$ (374.0)		$ (160.9)
Commodity Contracts - Financial [Member] | Minimum [Member] | Natural Gas [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MMBTU	2.41	[1]	2.55	[2]
Commodity Contracts - Financial [Member] | Minimum [Member] | NGL [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / gal	0.20	[1]	0.48	[2]
Commodity Contracts - Financial [Member] | Maximum [Member] | Natural Gas [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MMBTU	3.16	[1]	3.72	[2]
Commodity Contracts - Financial [Member] | Maximum [Member] | NGL [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / gal	0.99	[1]	1.14	[2]
Commodity Contracts - Financial [Member] | Weighted Average [Member] | Natural Gas [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MMBTU	2.84	[1]	3.04	[2]
Commodity Contracts - Financial [Member] | Weighted Average [Member] | NGL [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / gal	0.51	[1]	0.64	[2]
Commodity Contracts - Physical [Member] | Minimum [Member] | Natural Gas [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MMBTU	2.33	[1]	1.55	[2]
Commodity Contracts - Physical [Member] | Minimum [Member] | Crude Oil [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / bbl	31.17	[1]	49.57	[2]
Commodity Contracts - Physical [Member] | Minimum [Member] | NGL [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / gal	0.20	[1]	0.06	[2]
Commodity Contracts - Physical [Member] | Maximum [Member] | Natural Gas [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price	3.53	[1]	4.08	[2]
Commodity Contracts - Physical [Member] | Maximum [Member] | Crude Oil [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price	47.93	[1]	55.60	[2]
Commodity Contracts - Physical [Member] | Maximum [Member] | NGL [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price	1.39	[1]	1.21	[2]
Commodity Contracts - Physical [Member] | Weighted Average [Member] | Natural Gas [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MMBTU	2.61	[1]	3.08	[2]
Commodity Contracts - Physical [Member] | Weighted Average [Member] | Crude Oil [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / bbl	44.35	[1]	53.51	[2]
Commodity Contracts - Physical [Member] | Weighted Average [Member] | NGL [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / gal	0.43	[1]	0.54	[2]
Commodity Options [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Credit valuation adjustments	$ (0.4)		$ (0.7)
Commodity Options [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Option Volatility	10.00%	[1]	19.00%	[2]
Commodity Options [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Option Volatility	62.00%	[1]	94.00%	[2]
Commodity Options [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Option Volatility	35.00%	[1]	36.00%	[2]
Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets and liabilities accounted for at fair value on a recurring basis	$ 112.0	[3]	$ 168.9	[4]
Credit valuation adjustments	(0.3)		(1.0)
Level 3 [Member] | Commodity Contracts - Financial [Member] | Natural Gas [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets and liabilities accounted for at fair value on a recurring basis	0.3	[3]	0.6	[4]
Level 3 [Member] | Commodity Contracts - Financial [Member] | NGL [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets and liabilities accounted for at fair value on a recurring basis	14.0	[3]	42.1	[4]
Level 3 [Member] | Commodity Contracts - Physical [Member] | Natural Gas [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets and liabilities accounted for at fair value on a recurring basis	(3.9)	[3]	1.5	[4]
Level 3 [Member] | Commodity Contracts - Physical [Member] | Crude Oil [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets and liabilities accounted for at fair value on a recurring basis	(0.4)	[3]	(0.9)	[4]
Level 3 [Member] | Commodity Contracts - Physical [Member] | NGL [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets and liabilities accounted for at fair value on a recurring basis	8.9	[3]	18.9	[4]
Level 3 [Member] | Commodity Options [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets and liabilities accounted for at fair value on a recurring basis	$ 93.1	[3]	$ 106.7	[4]

[1] Prices are in dollars per Millions of British Thermal Units, or MMBtu, for natural gas; dollars per Gallon, or Gal, for NGLs; and dollars per barrel, or Bbl, for crude oil.

[2] Prices are in dollars per MMBtu for natural gas, Gal for NGLs and Bbl for crude oil.

[3] Fair values include credit valuation adjustment losses of approximately $0.3 million.

[4] Fair values include credit valuation adjustment losses of approximately $1.0 million.