SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,767,184	$ 1,817,061	$ 3,822,819	$ 4,330,491
Operating Income	423,422	412,015	911,958	909,490
Total Interest Expense	(100,492)	(92,259)	(198,703)	(187,102)
Other Income/(Loss), Net	8,038	12,899	10,049	18,626
Income Tax Expense	(125,439)	(123,268)	(271,742)	(276,494)
Net Income	205,529	209,387	451,562	464,520
Net Income Attributable to Noncontrolling Interests	(1,880)	(1,880)	(3,759)	(3,759)
Net Income Attributable to Controlling Interests	203,649	207,507	447,803	460,761
Total Assets	30,882,663		30,882,663		$ 30,580,309
Investments in Property, Plant and Equipment			869,168	740,379
Electric Distribution Member
Segment Reporting Information [Line Items]
Operating Revenues	1,303,100	1,382,700	2,739,200	3,142,800
Depreciation And Amortization	(98,400)	(98,500)	(226,100)	(257,600)
Operating Expenses, Other	(994,400)	(1,052,100)	(2,083,300)	(2,395,000)
Operating Income	210,300	232,100	429,800	490,200
Total Interest Expense	(47,600)	(45,600)	(95,600)	(93,200)
Other Income/(Loss), Net	6,300	5,500	6,300	7,600
Net Income Attributable to Controlling Interests	102,800	120,900	211,300	251,400
Total Assets	17,855,600		17,855,600		17,981,300
Investments in Property, Plant and Equipment			362,000	319,800
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	180,400	186,000	523,000	693,400
Depreciation And Amortization	(16,800)	(17,700)	(32,700)	(35,900)
Operating Expenses, Other	(141,100)	(150,200)	(374,500)	(538,700)
Operating Income	22,500	18,100	115,800	118,800
Total Interest Expense	(10,400)	(9,100)	(20,500)	(18,100)
Other Income/(Loss), Net	100	300	(200)	100
Net Income Attributable to Controlling Interests	8,000	5,300	58,900	61,000
Total Assets	3,122,500		3,122,500		3,104,500
Investments in Property, Plant and Equipment			105,000	67,500
Electric Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues	302,500	267,800	585,800	516,800
Depreciation And Amortization	(45,600)	(39,700)	(90,700)	(80,100)
Operating Expenses, Other	(82,500)	(73,100)	(155,500)	(147,200)
Operating Income	174,400	155,000	339,600	289,500
Total Interest Expense	(27,400)	(26,300)	(55,300)	(53,900)
Other Income/(Loss), Net	5,300	5,100	7,900	8,100
Net Income Attributable to Controlling Interests	92,500	80,400	178,200	147,000
Total Assets	8,376,200		8,376,200		8,019,300
Investments in Property, Plant and Equipment			349,100	328,700
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	211,100	203,700	425,300	443,700
Depreciation And Amortization	(7,500)	(7,100)	(14,400)	(14,300)
Operating Expenses, Other	(188,100)	(190,700)	(385,400)	(419,900)
Operating Income	15,500	5,900	25,500	9,500
Total Interest Expense	(16,600)	(12,400)	(30,700)	(24,100)
Other Income/(Loss), Net	219,000	220,100	524,400	535,000
Net Income Attributable to Controlling Interests	220,700	217,000	523,100	529,900
Total Assets	13,218,300		13,218,300		13,256,700
Investments in Property, Plant and Equipment			53,100	24,400
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(229,900)	(223,100)	(450,500)	(466,200)
Depreciation And Amortization	500	500	1,100	1,000
Operating Expenses, Other	230,100	223,500	450,700	466,700
Operating Income	700	900	1,300	1,500
Total Interest Expense	1,500	1,100	3,400	2,200
Other Income/(Loss), Net	(222,600)	(218,100)	(528,400)	(532,200)
Net Income Attributable to Controlling Interests	(220,400)	(216,100)	(523,700)	(528,500)
Total Assets	(11,689,900)		(11,689,900)		(11,781,500)
Investments in Property, Plant and Equipment			0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues	1,767,200	1,817,100	3,822,800	4,330,500
Depreciation And Amortization	(167,800)	(162,500)	(362,800)	(386,900)
Operating Expenses, Other	(1,176,000)	(1,242,600)	(2,548,000)	(3,034,100)
Operating Income	423,400	412,000	912,000	909,500
Total Interest Expense	(100,500)	(92,300)	(198,700)	(187,100)
Other Income/(Loss), Net	8,100	12,900	10,000	18,600
Net Income Attributable to Controlling Interests	203,600	$ 207,500	447,800	460,800
Total Assets	$ 30,882,700		30,882,700		$ 30,580,300
Investments in Property, Plant and Equipment			$ 869,200	$ 740,400