SEGMENT INFORMATION (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,635,862,000	$ 1,628,684,000	$ 3,630,885,000	$ 2,728,307,000
Operating Income	350,576,000	159,515,000	769,521,000	373,908,000
Total Interest Expense	(86,850,000)	(89,047,000)	(163,106,000)	(155,495,000)
Income Tax Expense	(95,606,000)	(26,055,000)	(216,093,000)	(82,019,000)
Net Income	173,064,000	46,219,000	403,032,000	146,974,000
Net Income Attributable to Noncontrolling Interests	(2,043,000)	(1,880,000)	(3,922,000)	(3,373,000)
Net Income Attributable to Controlling Interests	171,021,000	44,339,000	399,110,000	143,601,000
Total Assets	28,196,892,000		28,196,892,000		28,302,824,000
Investments in Property, Plant and Equipment			700,252,000	690,376,000
Electric Distribution Member
Segment Reporting Information [Line Items]
Operating Revenues	1,221,600,000	1,229,900,000	2,595,800,000	2,016,000,000
Depreciation And Amortization	(152,200,000)	(153,300,000)	(329,100,000)	(225,400,000)
Operating Expenses, Other	(883,300,000)	(1,004,800,000)	(1,888,300,000)	(1,627,000,000)
Operating Income	186,100,000	71,800,000	378,400,000	163,600,000
Total Interest Expense	(43,400,000)	(44,800,000)	(85,600,000)	(77,900,000)
Interest Income	1,000,000	1,000,000	2,100,000	2,100,000
Other Income/(Loss)	1,200,000	(200,000)	5,000,000	4,200,000
Income Tax Expense	(52,400,000)	(6,900,000)	(106,800,000)	(28,300,000)
Net Income	92,500,000	20,900,000	193,100,000	63,700,000
Net Income Attributable to Noncontrolling Interests	(1,300,000)	(1,200,000)	(2,500,000)	(2,000,000)
Net Income Attributable to Controlling Interests	91,200,000	19,700,000	190,600,000	61,700,000
Total Assets	18,138,700,000	15,161,300,000	18,138,700,000	15,161,300,000
Investments in Property, Plant and Equipment			315,300,000	305,700,000
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	154,100,000	133,500,000	515,900,000	272,500,000
Depreciation And Amortization	(16,700,000)	(12,400,000)	(34,100,000)	(20,100,000)
Operating Expenses, Other	(127,000,000)	(115,800,000)	(394,300,000)	(218,000,000)
Operating Income	10,400,000	5,300,000	87,500,000	34,400,000
Total Interest Expense	(8,900,000)	(8,800,000)	(16,200,000)	(14,300,000)
Interest Income	0	0	0	0
Other Income/(Loss)	100,000	100,000	300,000	100,000
Income Tax Expense	(400,000)	1,300,000	(27,100,000)	(7,600,000)
Net Income	1,200,000	(2,100,000)	44,500,000	12,600,000
Net Income Attributable to Noncontrolling Interests	0	0	0	0
Net Income Attributable to Controlling Interests	1,200,000	(2,100,000)	44,500,000	12,600,000
Total Assets	2,706,200,000	2,432,700,000	2,706,200,000	2,432,700,000
Investments in Property, Plant and Equipment			70,900,000	59,700,000
Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues	247,900,000	228,700,000	487,400,000	391,600,000
Depreciation And Amortization	(34,500,000)	(28,600,000)	(66,300,000)	(49,800,000)
Operating Expenses, Other	(63,600,000)	(65,500,000)	(125,800,000)	(113,200,000)
Operating Income	149,800,000	134,600,000	295,300,000	228,600,000
Total Interest Expense	(25,200,000)	(26,200,000)	(47,100,000)	(45,800,000)
Interest Income	400,000	100,000	500,000	300,000
Other Income/(Loss)	2,400,000	700,000	5,000,000	3,900,000
Income Tax Expense	(49,800,000)	(44,800,000)	(95,600,000)	(75,600,000)
Net Income	77,600,000	64,400,000	158,100,000	111,400,000
Net Income Attributable to Noncontrolling Interests	(800,000)	(700,000)	(1,400,000)	(1,400,000)
Net Income Attributable to Controlling Interests	76,800,000	63,700,000	156,700,000	110,000,000
Total Assets	6,429,700,000	5,327,700,000	6,429,700,000	5,327,700,000
Investments in Property, Plant and Equipment			297,400,000	297,200,000
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	220,700,000	230,200,000	437,800,000	363,400,000
Depreciation And Amortization	(21,700,000)	(17,700,000)	(40,800,000)	(21,600,000)
Operating Expenses, Other	(194,900,000)	(263,000,000)	(392,200,000)	(397,800,000)
Operating Income	4,100,000	(50,500,000)	4,800,000	(56,000,000)
Total Interest Expense	(10,700,000)	(11,100,000)	(17,100,000)	(20,400,000)
Interest Income	1,400,000	1,400,000	2,900,000	2,600,000
Other Income/(Loss)	230,800,000	117,900,000	551,100,000	240,500,000
Income Tax Expense	7,200,000	25,000,000	13,800,000	31,000,000
Net Income	232,800,000	82,700,000	555,500,000	197,700,000
Net Income Attributable to Noncontrolling Interests	0	0	0	0
Net Income Attributable to Controlling Interests	232,800,000	82,700,000	555,500,000	197,700,000
Total Assets	18,776,100,000	20,614,100,000	18,776,100,000	20,614,100,000
Investments in Property, Plant and Equipment			16,700,000	27,800,000
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(208,400,000)	(193,600,000)	(406,000,000)	(315,200,000)
Depreciation And Amortization	2,900,000	1,200,000	4,600,000	1,500,000
Operating Expenses, Other	205,700,000	190,700,000	404,900,000	317,000,000
Operating Income	200,000	(1,700,000)	3,500,000	3,300,000
Total Interest Expense	1,300,000	1,900,000	2,900,000	2,900,000
Interest Income	(1,600,000)	(1,400,000)	(3,200,000)	(2,700,000)
Other Income/(Loss)	(230,700,000)	(117,800,000)	(551,000,000)	(240,400,000)
Income Tax Expense	(200,000)	(700,000)	(400,000)	(1,500,000)
Net Income	(231,000,000)	(119,700,000)	(548,200,000)	(238,400,000)
Net Income Attributable to Noncontrolling Interests	0	0	0	0
Net Income Attributable to Controlling Interests	(231,000,000)	(119,700,000)	(548,200,000)	(238,400,000)
Total Assets	(17,853,800,000)	(16,029,500,000)	(17,853,800,000)	(16,029,500,000)
Investments in Property, Plant and Equipment			0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues	1,635,900,000	1,628,700,000	3,630,900,000	2,728,300,000
Depreciation And Amortization	(222,200,000)	(210,800,000)	(465,700,000)	(315,400,000)
Operating Expenses, Other	(1,063,100,000)	(1,258,400,000)	(2,395,700,000)	(2,039,000,000)
Operating Income	350,600,000	159,500,000	769,500,000	373,900,000
Total Interest Expense	(86,900,000)	(89,000,000)	(163,100,000)	(155,500,000)
Interest Income	1,200,000	1,100,000	2,300,000	2,300,000
Other Income/(Loss)	3,800,000	700,000	10,400,000	8,300,000
Income Tax Expense	(95,600,000)	(26,100,000)	(216,100,000)	(82,000,000)
Net Income	173,100,000	46,200,000	403,000,000	147,000,000
Net Income Attributable to Noncontrolling Interests	(2,100,000)	(1,900,000)	(3,900,000)	(3,400,000)
Net Income Attributable to Controlling Interests	171,000,000	44,300,000	399,100,000	143,600,000
Total Assets	28,196,900,000	27,506,300,000	28,196,900,000	27,506,300,000
Investments in Property, Plant and Equipment			$ 700,300,000	$ 690,400,000