SEGMENT INFORMATION (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenues	$ 2,513,431,000	$ 2,290,590,000
Operating Income	497,475,000	467,689,000
Total Interest Expense	(94,843,000)	(89,975,000)
Other Income/(Loss), Net	5,727,000	1,667,000
Income Tax Expense	(153,226,000)	(141,545,000)
Net Income	255,133,000	237,836,000
Net Income Attributable to Noncontrolling Interests	(1,879,000)	(1,879,000)
Net Income Attributable to Controlling Interests	253,254,000	235,957,000
Total Assets	29,951,765,000		29,777,975,000
Investments in Property, Plant and Equipment	362,586,000	348,691,000
Electric Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	1,760,100,000	1,585,900,000
Depreciation And Amortization	(159,100,000)	(148,800,000)
Operating Expenses, Other	(1,342,800,000)	(1,210,900,000)
Operating Income	258,200,000	226,200,000
Total Interest Expense	(47,600,000)	(47,400,000)
Other Income/(Loss), Net	2,200,000	1,400,000
Net Income Attributable to Controlling Interests	130,600,000	112,200,000
Total Assets	17,930,200,000		17,563,400,000
Investments in Property, Plant and Equipment	172,500,000	189,400,000
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	507,400,000	432,800,000
Depreciation And Amortization	(18,200,000)	(17,700,000)
Operating Expenses, Other	(388,500,000)	(321,400,000)
Operating Income	100,700,000	93,700,000
Total Interest Expense	(9,000,000)	(8,500,000)
Other Income/(Loss), Net	(200,000)	100,000
Net Income Attributable to Controlling Interests	55,600,000	52,100,000
Total Assets	3,008,500,000		3,030,900,000
Investments in Property, Plant and Equipment	30,000,000	28,900,000
Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues	249,000,000	252,100,000
Depreciation And Amortization	(40,400,000)	(37,000,000)
Operating Expenses, Other	(74,100,000)	(66,400,000)
Operating Income	134,500,000	148,700,000
Total Interest Expense	(27,600,000)	(25,500,000)
Other Income/(Loss), Net	2,900,000	1,500,000
Net Income Attributable to Controlling Interests	66,600,000	74,900,000
Total Assets	7,503,100,000		7,625,600,000
Investments in Property, Plant and Equipment	150,000,000	112,200,000
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	240,000,000	172,200,000
Depreciation And Amortization	(7,200,000)	(7,000,000)
Operating Expenses, Other	(229,200,000)	(165,400,000)
Operating Income	3,600,000	(200,000)
Total Interest Expense	(11,800,000)	(9,600,000)
Other Income/(Loss), Net	314,900,000	294,800,000
Net Income Attributable to Controlling Interests	312,900,000	291,700,000
Total Assets	12,874,100,000		12,682,500,000
Investments in Property, Plant and Equipment	10,100,000	18,200,000
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(243,100,000)	(152,400,000)
Depreciation And Amortization	500,000	1,800,000
Operating Expenses, Other	243,100,000	149,900,000
Operating Income	500,000	(700,000)
Total Interest Expense	1,200,000	1,000,000
Other Income/(Loss), Net	(314,100,000)	(296,100,000)
Net Income Attributable to Controlling Interests	(312,400,000)	(294,900,000)
Total Assets	(11,364,100,000)		(11,124,400,000)
Investments in Property, Plant and Equipment	0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues	2,513,400,000	2,290,600,000
Depreciation And Amortization	(224,400,000)	(208,700,000)
Operating Expenses, Other	(1,791,500,000)	(1,614,200,000)
Operating Income	497,500,000	467,700,000
Total Interest Expense	(94,800,000)	(90,000,000)
Other Income/(Loss), Net	5,700,000	1,700,000
Net Income Attributable to Controlling Interests	253,300,000	236,000,000
Total Assets	29,951,800,000		29,778,000,000
Investments in Property, Plant and Equipment	$ 362,600,000	$ 348,700,000