DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES (Fair Values of Expected Cash Flows of Commodity Based Swaps and Physical Contracts) (Details) $ in Millions		3 Months Ended
		Mar. 31, 2016 USD ($) MMBTU $ / MillionsofBTU-MMBTU $ / Barrel-bbl bbl	Dec. 31, 2015 USD ($)
Fair Value
Asset		$ 128.1	$ 163.6
Liability		$ (289.7)	(221.5)
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - Natural Gas [Member]
Derivative [Line Items]
Notional (MMBtu) | MMBTU	[1]	16,287
Fair Value
Asset	[2]	$ 0.0	0.0
Liability	[2]	$ 0.0	0.0
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - Natural Gas [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.43
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - Natural Gas [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	3.48
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - NGL [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	1,570,750
Fair Value
Asset	[2]	$ 1.8	0.2
Liability	[2]	$ (5.1)	(8.4)
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - NGL [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	23.30
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - NGL [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	25.39
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - Crude Oil [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	464,000
Fair Value
Asset	[2]	$ 0.1	0.0
Liability	[2]	$ (11.5)	(17.5)
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - Crude Oil [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	40.65
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - Crude Oil [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	65.19
Swaps - Portion of Contracts Maturing in 2016 - Receive Fixed/Pay Variable - NGL [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	1,894,000
Fair Value
Asset	[2]	$ 11.0	18.3
Liability	[2]	$ (1.4)	(0.2)
Swaps - Portion of Contracts Maturing in 2016 - Receive Fixed/Pay Variable - NGL [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	27.74
Swaps - Portion of Contracts Maturing in 2016 - Receive Fixed/Pay Variable - NGL [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	22.68
Swaps - Portion of Contracts Maturing in 2016 - Receive Fixed/Pay Variable - Crude Oil [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	970,575
Fair Value
Asset	[2]	$ 17.6	25.4
Liability	[2]	$ (0.6)	0.0
Swaps - Portion of Contracts Maturing in 2016 - Receive Fixed/Pay Variable - Crude Oil [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	58.65
Swaps - Portion of Contracts Maturing in 2016 - Receive Fixed/Pay Variable - Crude Oil [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	41.08
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - Natural Gas [Member]
Derivative [Line Items]
Notional (MMBtu) | MMBTU	[1]	7,355,000
Fair Value
Asset	[2]	$ 0.2	0.1
Liability	[2]	$ (0.2)	(0.1)
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - Natural Gas [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.47
Swaps - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - Natural Gas [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.47
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - NGL [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	890,000
Fair Value
Asset	[2]	$ 1.8	0.0
Liability	[2]	$ (0.1)	(0.2)
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - NGL [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	17.94
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Fixed - NGL [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	16.02
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive variable/pay fixed - Crude Oil [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	0
Fair Value
Asset	[2]	$ 0.0	0.0
Liability	[2]	$ 0.0	(0.2)
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive variable/pay fixed - Crude Oil [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	0
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive variable/pay fixed - Crude Oil [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	0
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Fixed/Pay Variable - NGL [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	869,166
Fair Value
Asset	[2]	$ 0.1	1.9
Liability	[2]	$ (2.3)	(0.2)
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Fixed/Pay Variable - NGL [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	22.46
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Fixed/Pay Variable - NGL [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	24.95
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - Natural Gas [Member]
Derivative [Line Items]
Notional (MMBtu) | MMBTU	[1]	118,233,634
Fair Value
Asset	[2]	$ 0.0	0.0
Liability	[2]	$ (2.1)	(2.8)
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - Natural Gas [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	1.94
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - Natural Gas [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	1.96
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - NGL [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	8,400,616
Fair Value
Asset	[2]	$ 3.7	4.0
Liability	[2]	$ (0.8)	(2.4)
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - NGL [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	16.85
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - NGL [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	16.51
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - Crude Oil [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	681,040
Fair Value
Asset	[2]	$ 0.7	0.7
Liability	[2]	$ (0.4)	(0.5)
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - Crude Oil [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	38.84
Physical Contracts - Portion of Contracts Maturing in 2016 - Receive Variable/Pay Variable - Crude Oil [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	38.38
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Fixed - Natural Gas [Member]
Derivative [Line Items]
Notional (MMBtu) | MMBTU	[1]	76,530
Fair Value
Asset	[2]	$ 0.0	0.0
Liability	[2]	$ 0.0	0.0
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Fixed - Natural Gas [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.49
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Fixed - Natural Gas [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.97
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Fixed - NGL [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	757,500
Fair Value
Asset	[2]	$ 0.1	0.0
Liability	[2]	$ (3.5)	(4.5)
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Fixed - NGL [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	16.63
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Fixed - NGL [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	21.05
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Fixed - Crude Oil [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	547,500
Fair Value
Asset	[2]	$ 0.0	0.0
Liability	[2]	$ (11.8)	(10.9)
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Fixed - Crude Oil [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	44.92
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Fixed - Crude Oil [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	66.72
Swaps - Portion of Contracts Maturing in 2017 - Receive Fixed/Pay Variable - NGL [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	757,500
Fair Value
Asset	[2]	$ 2.2	3.3
Liability	[2]	$ (0.3)	(0.1)
Swaps - Portion of Contracts Maturing in 2017 - Receive Fixed/Pay Variable - NGL [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	19.19
Swaps - Portion of Contracts Maturing in 2017 - Receive Fixed/Pay Variable - NGL [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	16.63
Swaps - Portion of Contracts Maturing in 2017 - Receive Fixed/Pay Variable - Crude Oil [Member]
Derivative [Line Items]
Notional (Bbl) | bbl	[1]	638,750
Fair Value
Asset	[2]	$ 11.9	10.9
Liability	[2]	$ 0.0	0.0
Swaps - Portion of Contracts Maturing in 2017 - Receive Fixed/Pay Variable - Crude Oil [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	63.63
Swaps - Portion of Contracts Maturing in 2017 - Receive Fixed/Pay Variable - Crude Oil [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl	[3]	44.92
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Variable - Natural Gas [Member]
Derivative [Line Items]
Notional (MMBtu) | MMBTU	[1]	12,550,000
Fair Value
Asset	[2]	$ 0.8	0.5
Liability	[2]	$ (0.2)	(0.2)
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Variable - Natural Gas [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.75
Swaps - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Variable - Natural Gas [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.70
Physical Contracts - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Variable - Natural Gas [Member]
Derivative [Line Items]
Notional (MMBtu) | MMBTU	[1]	3,987,810
Fair Value
Asset	[2]	$ 0.1	0.1
Liability	[2]	$ 0.0	0.0
Physical Contracts - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Variable - Natural Gas [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.78
Physical Contracts - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Variable - Natural Gas [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.75
Physical Contracts - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Variable - NGL [Member]
Derivative [Line Items]
Notional (Bbl) | bbl		186,500
Fair Value
Asset	[2]	$ 0.0	0.0
Liability	[2]	$ 0.0	0.0
Physical Contracts - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Variable - NGL [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl		23.33
Physical Contracts - Portion of Contracts Maturing in 2017 - Receive Variable/Pay Variable - NGL [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl		23.40
Physical Contracts - Portion of Contracts Maturing in 2018 - Receive Variable/Pay Variable - Natural Gas [Member]
Derivative [Line Items]
Notional (MMBtu) | MMBTU	[1]	2,187,810
Fair Value
Asset	[2]	$ 0.1	0.1
Liability	[2]	$ 0.0	0.0
Physical Contracts - Portion of Contracts Maturing in 2018 - Receive Variable/Pay Variable - Natural Gas [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.92
Physical Contracts - Portion of Contracts Maturing in 2018 - Receive Variable/Pay Variable - Natural Gas [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.89
Physical Contracts - Portion of Contracts Maturing in 2019 - Receive Variable/Pay Variable - Natural Gas [Member]
Derivative [Line Items]
Notional (MMBtu) | MMBTU	[1]	2,187,810
Fair Value
Asset	[2]	$ 0.1	0.1
Liability	[2]	$ 0.0	0.0
Physical Contracts - Portion of Contracts Maturing in 2019 - Receive Variable/Pay Variable - Natural Gas [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	3.00
Physical Contracts - Portion of Contracts Maturing in 2019 - Receive Variable/Pay Variable - Natural Gas [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	2.97
Physical Contracts - Portion of Contracts Maturing in 2020 - Receive Variable/Pay Variable - Natural Gas [Member]
Derivative [Line Items]
Notional (MMBtu) | MMBTU	[1]	359,640
Fair Value
Asset	[2]	$ 0.0	0.0
Liability	[2]	$ 0.0	0.0
Physical Contracts - Portion of Contracts Maturing in 2020 - Receive Variable/Pay Variable - Natural Gas [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	3.29
Physical Contracts - Portion of Contracts Maturing in 2020 - Receive Variable/Pay Variable - Natural Gas [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / MillionsofBTU-MMBTU	[3]	3.26
Physical Contracts - Portion of Contracts Maturing in 2017 - Receive Fixed/Pay Variable - NGL [Member]
Derivative [Line Items]
Notional (Bbl) | bbl		595
Fair Value
Asset	[2]	$ 0.0	0.0
Liability	[2]	$ 0.0	$ 0.0
Physical Contracts - Portion of Contracts Maturing in 2017 - Receive Fixed/Pay Variable - NGL [Member] | Receive [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl		22.37
Physical Contracts - Portion of Contracts Maturing in 2017 - Receive Fixed/Pay Variable - NGL [Member] | Pay [Member]
Derivative [Line Items]
Wtd. Average Price | $ / Barrel-bbl		21.17

[1] Volumes of natural gas are measured in MMBtu, whereas volumes of NGL and crude oil are measured in Bbl.

[2] The fair value is determined based on quoted market prices at March 31, 2016 and December 31, 2015, respectively, discounted using the swap rate for the respective periods to consider the time value of money. Fair values exclude credit valuation adjustment gains of approximately $0.4 million and $0.5 million at March 31, 2016 and December 31, 2015, respectively, as well as cash collateral received.

[3] Weighted-average prices received and paid are in $/MMBtu for natural gas and $/Bbl for NGL and crude oil.