SEGMENT INFORMATION (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,881,200,000	$ 1,892,500,000	$ 1,677,600,000	$ 2,290,600,000	$ 1,777,700,000	$ 1,892,600,000	$ 1,635,900,000	$ 1,995,000,000	$ 7,741,856,000	$ 7,301,204,000	$ 6,273,787,000
Operating Income	430,200,000	440,900,000	294,000,000	467,700,000	360,600,000	399,300,000	350,600,000	418,900,000	1,632,849,000	1,529,435,000	1,118,206,000
Total Interest Expense									(362,106,000)	(338,699,000)	(329,945,000)
Other Income/(Loss), Net									24,619,000	29,894,000	19,742,000
Income Tax Expense									(468,297,000)	(426,941,000)	(274,926,000)
Net Income	223,600,000	236,500,000	129,200,000	237,800,000	179,200,000	211,400,000	173,100,000	230,000,000	827,065,000	793,689,000	533,077,000
Net Income Attributable to Noncontrolling Interests									(7,519,000)	(7,682,000)	(7,132,000)
Net Income Attributable to Controlling Interests	221,500,000	234,600,000	127,400,000	236,000,000	177,400,000	209,500,000	171,000,000	228,100,000	819,546,000	786,007,000	525,945,000
Total Assets	29,777,975,000				27,795,537,000				29,777,975,000	27,795,537,000
Investments in Property, Plant and Equipment									1,603,744,000	1,456,787,000	1,472,272,000
Electric Distribution Member
Segment Reporting Information [Line Items]
Operating Revenues									5,663,400,000	5,362,300,000	4,716,500,000
Depreciation And Amortization									(384,600,000)	(604,800,000)	(530,300,000)
Operating Expenses, Other									(4,366,200,000)	(3,927,700,000)	(3,585,400,000)
Operating Income									912,600,000	829,800,000	600,800,000
Total Interest Expense									(191,600,000)	(175,000,000)	(165,600,000)
Interest Income									5,100,000	4,100,000	2,800,000
Other Income/(Loss) Excluding Interest Income									10,700,000	12,900,000	8,900,000
Income Tax Expense									(269,700,000)	(240,000,000)	(150,200,000)
Net Income									467,100,000	431,800,000	296,700,000
Net Income Attributable to Noncontrolling Interests									(4,700,000)	(4,800,000)	(4,400,000)
Net Income Attributable to Controlling Interests									462,400,000	427,000,000	292,300,000
Total Assets	17,563,400,000				17,260,000,000				17,563,400,000	17,260,000,000
Investments in Property, Plant and Equipment									645,200,000	639,000,000	611,700,000
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues									1,007,300,000	855,800,000	572,900,000
Depreciation And Amortization									(68,100,000)	(66,700,000)	(49,100,000)
Operating Expenses, Other									(786,700,000)	(659,400,000)	(445,200,000)
Operating Income									152,500,000	129,700,000	78,600,000
Total Interest Expense									(34,000,000)	(33,100,000)	(31,300,000)
Interest Income									0	0	0
Other Income/(Loss) Excluding Interest Income									200,000	800,000	400,000
Income Tax Expense									(46,400,000)	(36,500,000)	(16,900,000)
Net Income									72,300,000	60,900,000	30,800,000
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income Attributable to Controlling Interests									72,300,000	60,900,000	30,800,000
Total Assets	3,030,900,000				2,759,700,000				3,030,900,000	2,759,700,000
Investments in Property, Plant and Equipment									176,700,000	168,100,000	148,700,000
Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues									1,018,200,000	978,700,000	861,500,000
Depreciation And Amortization									(150,500,000)	(136,200,000)	(109,200,000)
Operating Expenses, Other									(302,100,000)	(281,800,000)	(251,600,000)
Operating Income									565,600,000	560,700,000	500,700,000
Total Interest Expense									(104,100,000)	(100,300,000)	(96,700,000)
Interest Income									900,000	700,000	400,000
Other Income/(Loss) Excluding Interest Income									10,300,000	10,900,000	7,300,000
Income Tax Expense									(174,500,000)	(182,100,000)	(159,200,000)
Net Income									298,200,000	289,900,000	252,500,000
Net Income Attributable to Noncontrolling Interests									(2,800,000)	(2,900,000)	(2,800,000)
Net Income Attributable to Controlling Interests									295,400,000	287,000,000	249,700,000
Total Assets	7,625,600,000				6,745,800,000				7,625,600,000	6,745,800,000
Investments in Property, Plant and Equipment									731,600,000	618,500,000	663,600,000
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues									790,900,000	777,500,000	803,800,000
Depreciation And Amortization									(42,100,000)	(62,200,000)	(56,400,000)
Operating Expenses, Other									(748,000,000)	(715,000,000)	(817,000,000)
Operating Income									800,000	300,000	(69,600,000)
Total Interest Expense									(36,600,000)	(35,500,000)	(43,600,000)
Interest Income									3,600,000	5,400,000	7,100,000
Other Income/(Loss) Excluding Interest Income									916,000,000	858,900,000	795,000,000
Income Tax Expense									22,300,000	31,900,000	55,500,000
Net Income									906,100,000	861,000,000	744,400,000
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income Attributable to Controlling Interests									906,100,000	861,000,000	744,400,000
Total Assets	12,682,500,000				11,842,400,000				12,682,500,000	11,842,400,000
Investments in Property, Plant and Equipment									50,200,000	31,200,000	48,300,000
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(737,900,000)	(673,100,000)	(680,900,000)
Depreciation And Amortization									19,900,000	10,200,000	4,200,000
Operating Expenses, Other									719,300,000	671,800,000	684,400,000
Operating Income									1,300,000	8,900,000	7,700,000
Total Interest Expense									4,200,000	5,200,000	7,300,000
Interest Income									(3,600,000)	(5,600,000)	(7,100,000)
Other Income/(Loss) Excluding Interest Income									(918,600,000)	(858,200,000)	(795,100,000)
Income Tax Expense									0	(200,000)	(4,100,000)
Net Income									(916,700,000)	(849,900,000)	(791,300,000)
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income Attributable to Controlling Interests									(916,700,000)	(849,900,000)	(791,300,000)
Total Assets	(11,124,400,000)				(10,812,400,000)				(11,124,400,000)	(10,812,400,000)
Investments in Property, Plant and Equipment									0	0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues									7,741,900,000	7,301,200,000	6,273,800,000
Depreciation And Amortization									(625,400,000)	(859,700,000)	(740,800,000)
Operating Expenses, Other									(5,483,700,000)	(4,912,100,000)	(4,414,800,000)
Operating Income									1,632,800,000	1,529,400,000	1,118,200,000
Total Interest Expense									(362,100,000)	(338,700,000)	(329,900,000)
Interest Income									6,000,000	4,600,000	3,200,000
Other Income/(Loss) Excluding Interest Income									18,600,000	25,300,000	16,500,000
Income Tax Expense									(468,300,000)	(426,900,000)	(274,900,000)
Net Income									827,000,000	793,700,000	533,100,000
Net Income Attributable to Noncontrolling Interests									(7,500,000)	(7,700,000)	(7,200,000)
Net Income Attributable to Controlling Interests									819,500,000	786,000,000	525,900,000
Total Assets	29,778,000,000				27,795,500,000				29,778,000,000	27,795,500,000
Investments in Property, Plant and Equipment									$ 1,603,700,000	$ 1,456,800,000	$ 1,472,300,000