SEGMENT INFORMATION (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,995,023,000	$ 1,099,623,000
Depreciation And Amortization	(243,500,000)	(104,600,000)
Operating Expenses, Other	(1,332,500,000)	(780,600,000)
Operating Income	418,945,000	214,393,000
Total Interest Expense	(76,255,000)	(66,447,000)
Income Tax Expense	(120,487,000)	(55,964,000)
Net Income	229,968,000	100,755,000
Net Income Attributable to Noncontrolling Interests	(1,879,000)	(1,493,000)
Net Income Attributable to Controlling Interests	228,089,000	99,262,000
Total Assets	28,328,661,000		28,302,824,000
Investments in Property, Plant and Equipment	388,950,000	304,294,000
Electric Distribution Member
Segment Reporting Information [Line Items]
Operating Revenues	1,374,200,000	786,000,000
Depreciation And Amortization	(177,000,000)	(72,200,000)
Operating Expenses, Other	(1,004,900,000)	(622,100,000)
Operating Income	192,300,000	91,700,000
Total Interest Expense	(42,100,000)	(33,000,000)
Interest Income	1,000,000	1,100,000
Other Income/(Loss)	3,800,000	4,400,000
Income Tax Expense	(54,300,000)	(21,400,000)
Net Income	100,700,000	42,800,000
Net Income Attributable to Noncontrolling Interests	(1,200,000)	(800,000)
Net Income Attributable to Controlling Interests	99,500,000	42,000,000
Total Assets	18,208,200,000	9,553,300,000
Investments in Property, Plant and Equipment	157,800,000	130,700,000
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	361,800,000	139,000,000
Depreciation And Amortization	(17,400,000)	(7,700,000)
Operating Expenses, Other	(267,200,000)	(102,200,000)
Operating Income	77,200,000	29,100,000
Total Interest Expense	(7,400,000)	(5,400,000)
Interest Income	0	0
Other Income/(Loss)	200,000	0
Income Tax Expense	(26,700,000)	(9,000,000)
Net Income	43,300,000	14,700,000
Net Income Attributable to Noncontrolling Interests	0	0
Net Income Attributable to Controlling Interests	43,300,000	14,700,000
Total Assets	2,735,400,000	1,498,200,000
Investments in Property, Plant and Equipment	31,200,000	20,500,000
Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues	239,500,000	162,800,000
Depreciation And Amortization	(31,800,000)	(21,100,000)
Operating Expenses, Other	(62,200,000)	(47,600,000)
Operating Income	145,500,000	94,100,000
Total Interest Expense	(21,900,000)	(19,700,000)
Interest Income	100,000	100,000
Other Income/(Loss)	2,700,000	3,300,000
Income Tax Expense	(45,800,000)	(30,800,000)
Net Income	80,600,000	47,000,000
Net Income Attributable to Noncontrolling Interests	(700,000)	(700,000)
Net Income Attributable to Controlling Interests	79,900,000	46,300,000
Total Assets	6,269,100,000	3,900,700,000
Investments in Property, Plant and Equipment	185,400,000	135,900,000
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	217,200,000	133,300,000
Depreciation And Amortization	(19,000,000)	(3,900,000)
Operating Expenses, Other	(197,400,000)	(134,900,000)
Operating Income	800,000	(5,500,000)
Total Interest Expense	(6,400,000)	(9,400,000)
Interest Income	1,600,000	1,300,000
Other Income/(Loss)	320,300,000	122,600,000
Income Tax Expense	6,500,000	6,000,000
Net Income	322,800,000	115,000,000
Net Income Attributable to Noncontrolling Interests	0	0
Net Income Attributable to Controlling Interests	322,800,000	115,000,000
Total Assets	18,749,800,000	7,261,700,000
Investments in Property, Plant and Equipment	14,600,000	17,200,000
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(197,700,000)	(121,500,000)
Depreciation And Amortization	1,700,000	300,000
Operating Expenses, Other	199,200,000	126,200,000
Operating Income	3,200,000	5,000,000
Total Interest Expense	1,500,000	1,100,000
Interest Income	(1,600,000)	(1,300,000)
Other Income/(Loss)	(320,300,000)	(122,700,000)
Income Tax Expense	(200,000)	(800,000)
Net Income	(317,400,000)	(118,700,000)
Net Income Attributable to Noncontrolling Interests	0	0
Net Income Attributable to Controlling Interests	(317,400,000)	(118,700,000)
Total Assets	(17,633,800,000)	(6,235,500,000)
Investments in Property, Plant and Equipment	0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues	1,995,000,000	1,099,600,000
Operating Income	419,000,000	214,400,000
Total Interest Expense	(76,300,000)	(66,400,000)
Interest Income	1,100,000	1,200,000
Other Income/(Loss)	6,700,000	7,600,000
Income Tax Expense	(120,500,000)	(56,000,000)
Net Income	230,000,000	100,800,000
Net Income Attributable to Noncontrolling Interests	(1,900,000)	(1,500,000)
Net Income Attributable to Controlling Interests	228,100,000	99,300,000
Total Assets	28,328,700,000	15,978,400,000
Investments in Property, Plant and Equipment	$ 389,000,000	$ 304,300,000