FAIR VALUE (Details 4) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of the period	$ 5,700,000	$ (13,400,000)	$ (4,900,000)	$ (7,900,000)
Net realized and unrealized (losses) gains included in earnings	7,400,000	4,300,000	10,600,000	(1,900,000)
Net unrealized (losses) gains recorded as regulatory assets or liabilities	(3,900,000)	1,900,000	1,900,000	1,600,000
Purchases	700,000		6,500,000	7,000,000
Sales			(100,000)	(100,000)
Settlements	(4,300,000)	(8,800,000)	(10,700,000)	(11,200,000)
Net transfers into Level 3	2,300,000	1,400,000	10,000,000	(4,600,000)
Net transfers out of Level 3	500,000	1,600,000	(4,900,000)	4,100,000
Balance at the end of the period	8,400,000	(13,000,000)	8,400,000	(13,000,000)
Net unrealized (losses) gains included in earnings related to instruments still held at the end of the period	6,100,000	5,300,000	8,900,000	(3,400,000)
Nonregulated Segments | Natural gas contracts
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of the period	7,700,000	6,300,000	3,900,000	8,300,000
Net realized and unrealized (losses) gains included in earnings	4,200,000	2,700,000	1,300,000	1,900,000
Net unrealized (losses) gains recorded as regulatory assets or liabilities	0	0	0	0
Purchases	0		7,000,000	0
Sales			0	0
Settlements	(2,500,000)	(6,700,000)	(4,300,000)	(9,300,000)
Net transfers into Level 3	2,500,000	400,000	4,000,000	3,200,000
Net transfers out of Level 3	(300,000)	(300,000)	(300,000)	(1,700,000)
Balance at the end of the period	11,600,000	2,400,000	11,600,000	2,400,000
Net unrealized (losses) gains included in earnings related to instruments still held at the end of the period	4,200,000	2,700,000	1,300,000	1,900,000
Nonregulated Segments | Electric contracts
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Net unrealized loss related to discontinued operations		200,000		600,000
Balance at the beginning of the period	4,100,000	(14,700,000)	(4,300,000)	(11,500,000)
Net realized and unrealized (losses) gains included in earnings	1,900,000	2,600,000	7,600,000	(5,300,000)
Net unrealized (losses) gains recorded as regulatory assets or liabilities	0	0	0	0
Purchases	700,000		2,300,000	2,100,000
Sales			0	0
Settlements	(4,600,000)	(100,000)	(4,300,000)	7,400,000
Net transfers into Level 3	(200,000)	1,000,000	6,000,000	(7,800,000)
Net transfers out of Level 3	800,000	1,900,000	(4,600,000)	5,800,000
Balance at the end of the period	2,700,000	(9,300,000)	2,700,000	(9,300,000)
Net unrealized (losses) gains included in earnings related to instruments still held at the end of the period	1,900,000	2,600,000	7,600,000	(5,300,000)
Nonregulated Segments | Contingent consideration
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of the period	(7,700,000)		0
Net realized and unrealized (losses) gains included in earnings	0		0
Net unrealized (losses) gains recorded as regulatory assets or liabilities	0		0
Purchases	0		(7,700,000)
Sales			0
Settlements	0		0
Net transfers into Level 3	0		0
Net transfers out of Level 3	0		0
Balance at the end of the period	(7,700,000)		(7,700,000)
Net unrealized (losses) gains included in earnings related to instruments still held at the end of the period	0		0
Utility Segments
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Unrealized gain (loss) included in income	0	0	0	0
Utility Segments | FTRs
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of the period	3,900,000	4,800,000	2,000,000	2,200,000
Net realized and unrealized (losses) gains included in earnings	1,300,000	(1,000,000)	1,700,000	1,500,000
Net unrealized (losses) gains recorded as regulatory assets or liabilities	600,000	(200,000)	(300,000)	100,000
Purchases	0		4,900,000	4,900,000
Sales			(100,000)	(100,000)
Settlements	(2,800,000)	(400,000)	(5,200,000)	(5,400,000)
Net transfers into Level 3	0	0	0	0
Net transfers out of Level 3	0	0	0	0
Balance at the end of the period	3,000,000	3,200,000	3,000,000	3,200,000
Net unrealized (losses) gains included in earnings related to instruments still held at the end of the period	0	0	0	0
Utility Segments | Coal contracts
Changes in the fair value of items measured on a recurring basis and categorized as Level 3 measurements
Balance at the beginning of the period	(2,300,000)	(9,800,000)	(6,500,000)	(6,900,000)
Net realized and unrealized (losses) gains included in earnings	0	0	0	0
Net unrealized (losses) gains recorded as regulatory assets or liabilities	(4,500,000)	2,100,000	2,200,000	1,500,000
Purchases	0		0	0
Sales			0	0
Settlements	5,600,000	(1,600,000)	3,100,000	(3,900,000)
Net transfers into Level 3	0	0	0	0
Net transfers out of Level 3	0	0	0	0
Balance at the end of the period	(1,200,000)	(9,300,000)	(1,200,000)	(9,300,000)
Net unrealized (losses) gains included in earnings related to instruments still held at the end of the period	$ 0	$ 0	$ 0	$ 0