DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES (Quantitative Information about Level 3 Fair Value Measurements) (Details) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2016 USD ($) $ / Gallon-gal $ / MillionsofBTU-MMBTU $ / Barrel-bbl $ / MillionBarrels-MMBbls	Dec. 31, 2015 USD ($) $ / Gallon-gal $ / MillionsofBTU-MMBTU $ / Barrel-bbl
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets and liabilities accounted for at fair value on a recurring basis	[1]	$ (161.6)	$ (57.9)
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	[2]	77.4	103.8
Credit Valuation Adjustments		0.2	0.3
Commodity Contracts - Financial [Member] | Natural Gas [Member] | 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	[2]	0.6	0.3
Commodity Contracts - Financial [Member] | NGL [Member] | 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	[2]	$ 4.9	$ 8.6
Commodity Contracts - Financial [Member] | Maximum [Member] | Natural Gas [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MillionsofBTU-MMBTU	[3]	3.27	3.07
Commodity Contracts - Financial [Member] | Maximum [Member] | NGL [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / Gallon-gal	[3]	0.92	0.93
Commodity Contracts - Financial [Member] | Minimum [Member] | Natural Gas [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price	[3]	1.80	2.27
Commodity Contracts - Financial [Member] | Minimum [Member] | NGL [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / Gallon-gal	[3]	0.17	0.16
Commodity Contracts - Financial [Member] | Weighted Average [Member] | Natural Gas [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MillionsofBTU-MMBTU	[3]	2.69	2.64
Commodity Contracts - Financial [Member] | Weighted Average [Member] | NGL [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / Gallon-gal	[3]	0.42	0.41
Commodity Contracts - Physical [Member] | Natural Gas [Member] | 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	[2]	$ (1.8)	$ (2.5)
Commodity Contracts - Physical [Member] | Crude Oil [Member] | 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	[2]	0.3	0.0
Commodity Contracts - Physical [Member] | NGL [Member] | 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	[2]	$ 2.4	$ 3.1
Commodity Contracts - Physical [Member] | Maximum [Member] | Natural Gas [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MillionsofBTU-MMBTU	[3]	3.27	3.44
Commodity Contracts - Physical [Member] | Maximum [Member] | Crude Oil [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / Barrel-bbl	[3]	40.90	38.41
Commodity Contracts - Physical [Member] | Maximum [Member] | NGL [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / Gallon-gal	[3]	0.92	1.20
Commodity Contracts - Physical [Member] | Minimum [Member] | Natural Gas [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MillionsofBTU-MMBTU	[3]	1.53	2.08
Commodity Contracts - Physical [Member] | Minimum [Member] | Crude Oil [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / Barrel-bbl	[3]	28.29	26.50
Commodity Contracts - Physical [Member] | Minimum [Member] | NGL [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / Gallon-gal	[3]	0.17	0.16
Commodity Contracts - Physical [Member] | Weighted Average [Member] | Natural Gas [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / MillionsofBTU-MMBTU	[3]	2.01	2.33
Commodity Contracts - Physical [Member] | Weighted Average [Member] | Crude Oil [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / Barrel-bbl	[3]	38.91	37.29
Commodity Contracts - Physical [Member] | Weighted Average [Member] | NGL [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Forward Price | $ / Gallon-gal	[3]	0.41	0.40
Commodity Option [Member] | 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	[2]	$ 71.0	$ 94.3
Commodity Option [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Option Volatility	[3]	100.00%	74.00%
Commodity Option [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Option Volatility	[3]	8.00%	13.00%
Commodity Option [Member] | Weighted Average [Member] | Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Option Volatility	[3]	37.00%	36.00%

[1] As determined by nationally-recognized statistical ratings organizations.

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

[3] 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.