SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,933,105	$ 1,892,532	$ 6,263,597	$ 5,860,736
Operating Income	469,238	440,910	1,378,728	1,202,588
Total Interest Expense	(92,534)	(89,738)	(279,635)	(272,208)
Other Income/(Loss), Net	5,241	11,860	23,866	19,054
Income Tax Expense	(144,146)	(126,539)	(420,640)	(345,858)
Net Income	237,799	236,493	702,319	603,576
Net Income Attributable to Noncontrolling Interests	(1,879)	(1,879)	(5,639)	(5,639)
Net Income Attributable to Controlling Interests	235,920	234,614	696,680	597,937
Total Assets	30,046,026		30,046,026		$ 29,777,975
Investments in Property, Plant and Equipment			1,177,285	1,117,493
Electric Distribution Member
Segment Reporting Information [Line Items]
Operating Revenues	1,543,700	1,502,600	4,686,500	4,350,400
Depreciation And Amortization	(84,500)	(71,700)	(342,100)	(309,900)
Operating Expenses, Other	(1,140,800)	(1,141,500)	(3,535,700)	(3,343,900)
Operating Income	318,400	289,400	808,700	696,600
Total Interest Expense	(47,400)	(49,200)	(140,600)	(143,800)
Other Income/(Loss), Net	1,900	9,300	9,600	13,600
Net Income Attributable to Controlling Interests	167,500	153,400	418,900	349,100
Total Assets	17,836,800		17,836,800		17,563,400
Investments in Property, Plant and Equipment			506,500	480,100
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	106,200	109,200	799,600	737,500
Depreciation And Amortization	(17,500)	(16,400)	(53,400)	(51,100)
Operating Expenses, Other	(92,700)	(98,400)	(631,500)	(586,200)
Operating Income	(4,000)	(5,600)	114,700	100,200
Total Interest Expense	(9,200)	(8,500)	(27,200)	(25,600)
Other Income/(Loss), Net	(200)	100	(100)	200
Net Income Attributable to Controlling Interests	(3,700)	(9,900)	57,300	44,200
Total Assets	2,986,000		2,986,000		3,030,900
Investments in Property, Plant and Equipment			120,000	120,600
Electric Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues	270,400	262,500	787,200	721,400
Depreciation And Amortization	(42,400)	(37,400)	(122,600)	(111,400)
Operating Expenses, Other	(78,300)	(74,200)	(225,500)	(211,500)
Operating Income	149,700	150,900	439,100	398,500
Total Interest Expense	(25,900)	(24,500)	(79,800)	(78,800)
Other Income/(Loss), Net	3,800	2,700	11,900	6,900
Net Income Attributable to Controlling Interests	78,000	88,100	225,000	206,800
Total Assets	7,773,700		7,773,700		7,625,600
Investments in Property, Plant and Equipment			493,900	469,900
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	211,600	211,200	655,200	568,100
Depreciation And Amortization	(7,100)	(13,800)	(21,500)	(28,300)
Operating Expenses, Other	(199,600)	(192,400)	(619,400)	(534,100)
Operating Income	4,900	5,000	14,300	5,700
Total Interest Expense	(11,200)	(8,600)	(35,400)	(27,200)
Other Income/(Loss), Net	241,900	226,400	777,000	657,900
Net Income Attributable to Controlling Interests	234,900	228,300	764,700	653,400
Total Assets	12,750,000		12,750,000		12,682,500
Investments in Property, Plant and Equipment			56,900	46,900
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(198,800)	(193,000)	(664,900)	(516,700)
Depreciation And Amortization	500	8,600	1,600	12,700
Operating Expenses, Other	198,500	185,600	665,200	505,600
Operating Income	200	1,200	1,900	1,600
Total Interest Expense	1,200	1,000	3,400	3,200
Other Income/(Loss), Net	(242,200)	(226,600)	(774,500)	(659,500)
Net Income Attributable to Controlling Interests	(240,800)	(225,300)	(769,200)	(655,600)
Total Assets	(11,300,500)		(11,300,500)		(11,124,400)
Investments in Property, Plant and Equipment			0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues	1,933,100	1,892,500	6,263,600	5,860,700
Depreciation And Amortization	(151,000)	(130,700)	(538,000)	(488,000)
Operating Expenses, Other	(1,312,900)	(1,320,900)	(4,346,900)	(4,170,100)
Operating Income	469,200	440,900	1,378,700	1,202,600
Total Interest Expense	(92,500)	(89,800)	(279,600)	(272,200)
Other Income/(Loss), Net	5,200	11,900	23,900	19,100
Net Income Attributable to Controlling Interests	235,900	$ 234,600	696,700	597,900
Total Assets	$ 30,046,000		30,046,000		$ 29,778,000
Investments in Property, Plant and Equipment			$ 1,177,300	$ 1,117,500