SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating Revenues	$ 2,055,635	$ 2,513,431
Operating Income	488,536	497,475
Total Interest Expense	(98,212)	(94,843)
Other Income/(Loss), Net	2,011	5,727
Income Tax Expense	(146,302)	(153,226)
Net Income	246,033	255,133
Net Income Attributable to Noncontrolling Interests	(1,880)	(1,879)
Net Income Attributable to Controlling Interests	244,153	253,254
Total Assets	30,712,475		$ 30,580,309
Investments in Property, Plant and Equipment	431,472	362,586
Electric Distribution Member
Segment Reporting Information [Line Items]
Operating Revenues	1,436,100	1,760,100
Depreciation And Amortization	(127,700)	(159,100)
Operating Expenses, Other	(1,088,900)	(1,342,800)
Operating Income	219,500	258,200
Total Interest Expense	(48,000)	(47,600)
Other Income/(Loss), Net	0	2,200
Net Income Attributable to Controlling Interests	108,400	130,600
Total Assets	17,999,800		17,981,300
Investments in Property, Plant and Equipment	184,200	172,500
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	342,600	507,400
Depreciation And Amortization	(15,800)	(18,200)
Operating Expenses, Other	(233,500)	(388,500)
Operating Income	93,300	100,700
Total Interest Expense	(10,100)	(9,000)
Other Income/(Loss), Net	(300)	(200)
Net Income Attributable to Controlling Interests	50,900	55,600
Total Assets	3,134,100		3,104,500
Investments in Property, Plant and Equipment	52,100	30,000
Electric Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues	283,300	249,000
Depreciation And Amortization	(45,100)	(40,400)
Operating Expenses, Other	(73,000)	(74,100)
Operating Income	165,200	134,500
Total Interest Expense	(28,000)	(27,600)
Other Income/(Loss), Net	2,600	2,900
Net Income Attributable to Controlling Interests	85,700	66,600
Total Assets	8,127,200		8,019,300
Investments in Property, Plant and Equipment	172,400	150,000
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	214,200	240,000
Depreciation And Amortization	(6,900)	(7,200)
Operating Expenses, Other	(197,300)	(229,200)
Operating Income	10,000	3,600
Total Interest Expense	(14,100)	(11,800)
Other Income/(Loss), Net	305,500	314,900
Net Income Attributable to Controlling Interests	302,500	312,900
Total Assets	13,335,600		13,256,700
Investments in Property, Plant and Equipment	22,800	10,100
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(220,600)	(243,100)
Depreciation And Amortization	500	500
Operating Expenses, Other	220,600	243,100
Operating Income	500	500
Total Interest Expense	2,000	1,200
Other Income/(Loss), Net	(305,800)	(314,100)
Net Income Attributable to Controlling Interests	(303,300)	(312,400)
Total Assets	(11,884,200)		(11,781,500)
Investments in Property, Plant and Equipment	0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues	2,055,600	2,513,400
Depreciation And Amortization	(195,000)	(224,400)
Operating Expenses, Other	(1,372,100)	(1,791,500)
Operating Income	488,500	497,500
Total Interest Expense	(98,200)	(94,800)
Other Income/(Loss), Net	2,000	5,700
Net Income Attributable to Controlling Interests	244,200	253,300
Total Assets	30,712,500		$ 30,580,300
Investments in Property, Plant and Equipment	$ 431,500	$ 362,600