SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,817,061	$ 1,677,614	$ 4,330,491	$ 3,968,204
Operating Income	412,015	293,990	909,490	761,679
Total Interest Expense	(92,259)	(92,495)	(187,102)	(182,471)
Other Income/(Loss), Net	12,899	5,526	18,626	7,194
Income Tax Expense	(123,268)	(77,774)	(276,494)	(219,319)
Net Income	209,387	129,247	464,520	367,083
Net Income Attributable to Noncontrolling Interests	(1,880)	(1,880)	(3,759)	(3,759)
Net Income Attributable to Controlling Interests	207,507	127,367	460,761	363,324
Total Assets	29,879,939		29,879,939		$ 29,777,975
Investments in Property, Plant and Equipment			740,379	724,043
Electric Distribution Member
Segment Reporting Information [Line Items]
Operating Revenues	1,382,700	1,261,800	3,142,800	2,847,800
Depreciation And Amortization	(98,500)	(89,300)	(257,600)	(238,200)
Operating Expenses, Other	(1,052,100)	(991,500)	(2,395,000)	(2,202,400)
Operating Income	232,100	181,000	490,200	407,200
Total Interest Expense	(45,600)	(47,200)	(93,200)	(94,600)
Other Income/(Loss), Net	5,500	2,900	7,600	4,300
Net Income Attributable to Controlling Interests	120,900	83,400	251,400	195,600
Total Assets	17,872,900		17,872,900		17,563,400
Investments in Property, Plant and Equipment			319,800	335,600
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	186,000	195,500	693,400	628,300
Depreciation And Amortization	(17,700)	(16,900)	(35,900)	(34,600)
Operating Expenses, Other	(150,200)	(166,500)	(538,700)	(487,900)
Operating Income	18,100	12,100	118,800	105,800
Total Interest Expense	(9,100)	(8,700)	(18,100)	(17,100)
Other Income/(Loss), Net	300	0	100	100
Net Income Attributable to Controlling Interests	5,300	2,000	61,000	54,100
Total Assets	2,933,400		2,933,400		3,030,900
Investments in Property, Plant and Equipment			67,500	68,600
Electric Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues	267,800	206,900	516,800	458,900
Depreciation And Amortization	(39,700)	(37,000)	(80,100)	(74,000)
Operating Expenses, Other	(73,100)	(71,000)	(147,200)	(137,300)
Operating Income	155,000	98,900	289,500	247,600
Total Interest Expense	(26,300)	(28,800)	(53,900)	(54,300)
Other Income/(Loss), Net	5,100	2,700	8,100	4,200
Net Income Attributable to Controlling Interests	80,400	43,900	147,000	118,800
Total Assets	7,589,700		7,589,700		7,625,600
Investments in Property, Plant and Equipment			328,700	289,300
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	203,700	184,700	443,700	356,900
Depreciation And Amortization	(7,100)	(7,700)	(14,300)	(14,700)
Operating Expenses, Other	(190,700)	(174,900)	(419,900)	(340,300)
Operating Income	5,900	2,100	9,500	1,900
Total Interest Expense	(12,400)	(9,100)	(24,100)	(18,700)
Other Income/(Loss), Net	220,100	137,700	535,000	432,400
Net Income Attributable to Controlling Interests	217,000	133,300	529,900	424,900
Total Assets	12,455,700		12,455,700		12,682,500
Investments in Property, Plant and Equipment			24,400	30,500
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(223,100)	(171,300)	(466,200)	(323,700)
Depreciation And Amortization	500	2,300	1,000	4,100
Operating Expenses, Other	223,500	168,900	466,700	318,800
Operating Income	900	(100)	1,500	(800)
Total Interest Expense	1,100	1,300	2,200	2,200
Other Income/(Loss), Net	(218,100)	(137,800)	(532,200)	(433,800)
Net Income Attributable to Controlling Interests	(216,100)	(135,200)	(528,500)	(430,100)
Total Assets	(10,971,800)		(10,971,800)		(11,124,400)
Investments in Property, Plant and Equipment			0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues	1,817,100	1,677,600	4,330,500	3,968,200
Depreciation And Amortization	(162,500)	(148,600)	(386,900)	(357,400)
Operating Expenses, Other	(1,242,600)	(1,235,000)	(3,034,100)	(2,849,100)
Operating Income	412,000	294,000	909,500	761,700
Total Interest Expense	(92,300)	(92,500)	(187,100)	(182,500)
Other Income/(Loss), Net	12,900	5,500	18,600	7,200
Net Income Attributable to Controlling Interests	207,500	$ 127,400	460,800	363,300
Total Assets	$ 29,879,900		29,879,900		$ 29,778,000
Investments in Property, Plant and Equipment			$ 740,400	$ 724,000