DERIVATIVE INSTRUMENTS (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010		Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	$ 31,959,000				$ 31,959,000				$ 51,069,000
Fair value Derivative Liabilities	30,326,000				30,326,000				58,342,000
Interest Rate Contracts [Abstract]
Losses recognized in OCI on effective portion	(462,000)		(387,000)		(642,000)		(314,000)
Losses reclassified from accumulated OCI into income	(377,000)	[1]	(235,000)	[1]	(737,000)	[1]	(468,000)	[1]
Gains or (losses) recognized in income on ineffective portion	0	[1]	0	[1]	0	[1]	0	[1]
Gain (loss) on energy related derivative instruments not designated as hedging instruments	1,657,000	[2]	4,207,000	[2]	6,132,000	[2]	(17,917,000)
Gain (loss) on interest rate derivative instruments not designated as hedging instruments	(250,000)	[1]	(600,000)	[1]	11,000	[1]	(838,000)
Derivative instruments not designated as hedging instruments, gain (loss), net	1,407,000		3,607,000		6,143,000		(18,755,000)
Realized losses, derivative instruments on energy-related contracts	2,500,000		8,200,000		7,100,000		12,300,000
Fair value derivative instruments with credit-risk-related features	7,700,000				7,700,000
Additional collateral, aggregate fair value	2,400,000				2,400,000
Natural Gas (in MMdts) [Member] | Derivative Transaction Type, Purchase [Member]
Derivative [Line Items]
Outstanding derivative contracts notional amount	13.8				13.8
Natural Gas (in MMdts) [Member] | Derivative Transaction Type, Sale [Member]
Derivative [Line Items]
Outstanding derivative contracts notional amount	12.4				12.4
Electricity (in MMmwh) [Member] | Derivative Transaction Type, Purchase [Member]
Derivative [Line Items]
Outstanding derivative contracts notional amount	1.7				1.7
Electricity (in MMmwh) [Member] | Derivative Transaction Type, Sale [Member]
Derivative [Line Items]
Outstanding derivative contracts notional amount	0.1				0.1
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Derivatives-Energy Related-Current [Member]
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	25,347,000				25,347,000				39,513,000
Fair value Derivative Liabilities	18,619,000				18,619,000				42,297,000
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Derivatives-Energy Related-NonCurrent [Member]
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	6,612,000				6,612,000				11,556,000
Fair value Derivative Liabilities	4,214,000				4,214,000				8,641,000
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Derivatives-Other [Member]
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	0				0				0
Fair value Derivative Liabilities	5,639,000				5,639,000				5,539,000
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Derivatives-Other [Member]
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	0				0				0
Fair value Derivative Liabilities	1,854,000				1,854,000				1,865,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	31,959,000				31,959,000				51,069,000
Fair value Derivative Liabilities	28,472,000				28,472,000				56,477,000
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value Derivative Assets	0				0				0
Fair value Derivative Liabilities	$ 1,854,000				$ 1,854,000				$ 1,865,000

[1] Included in Interest Charges

[2] Included in Operating Revenues - Non Utility