SEGMENT INFORMATION - Summary of Segment Information and Segmented Total Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Operating Revenues	$ 2,572,641	$ 2,122,538	$ 6,043,951	$ 4,948,378
Depreciation and Amortization	(364,600)	(280,200)	(891,000)	(659,000)
Other Operating Expenses	(1,752,400)	(1,390,700)	(4,034,400)	(3,252,200)
Operating Income	455,569	451,605	1,118,623	1,037,173
Interest Expense	(160,090)	(145,435)	(313,334)	(283,201)
Other Income, Net	93,861	46,619	165,422	80,820
Net Income Attributable to Common Shareholders	291,862	264,520	735,309	630,663
Cash Flows Used for Investments in Plant			1,549,081	1,423,223
Assets	49,916,240		49,916,240		$ 48,492,144
Other
Segment Reporting Information [Line Items]
Operating Revenues	335,700	330,000	719,300	673,000
Depreciation and Amortization	(33,200)	(28,400)	(63,400)	(55,700)
Other Operating Expenses	(279,400)	(285,700)	(610,900)	(585,200)
Operating Income	23,100	15,900	45,000	32,100
Interest Expense	(53,500)	(41,800)	(100,300)	(83,400)
Other Income, Net	354,300	309,200	850,200	733,400
Net Income Attributable to Common Shareholders	316,000	282,700	784,700	677,600
Cash Flows Used for Investments in Plant			122,700	109,900
Assets	23,833,900		23,833,900		22,674,700
Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	(695,900)	(659,800)	(1,405,700)	(1,304,900)
Depreciation and Amortization	1,600	1,100	3,300	2,100
Other Operating Expenses	692,100	660,300	1,400,800	1,305,200
Operating Income	(2,200)	1,600	(1,600)	2,400
Interest Expense	16,300	12,800	26,400	24,400
Other Income, Net	(335,400)	(304,800)	(828,500)	(725,800)
Net Income Attributable to Common Shareholders	(321,300)	(290,400)	(803,700)	(699,000)
Cash Flows Used for Investments in Plant			0	0
Assets	(23,038,200)		(23,038,200)		(21,738,600)
Electric Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	2,004,400	1,676,500	4,390,700	3,576,900
Depreciation and Amortization	(198,100)	(132,300)	(549,700)	(354,300)
Other Operating Expenses	(1,636,100)	(1,360,300)	(3,481,700)	(2,890,800)
Operating Income	170,200	183,900	359,300	331,800
Interest Expense	(60,300)	(61,100)	(119,800)	(114,400)
Other Income, Net	53,000	29,900	100,500	50,600
Net Income Attributable to Common Shareholders	129,000	121,600	269,900	214,900
Cash Flows Used for Investments in Plant			541,800	510,400
Assets	26,238,100		26,238,100		25,411,200
Natural Gas Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	416,200	311,800	1,343,800	1,092,300
Depreciation and Amortization	(39,100)	(34,600)	(91,100)	(80,300)
Other Operating Expenses	(360,700)	(257,700)	(1,018,000)	(793,600)
Operating Income	16,400	19,500	234,700	218,400
Interest Expense	(16,700)	(14,600)	(32,500)	(28,500)
Other Income, Net	10,600	4,600	20,800	8,500
Net Income Attributable to Common Shareholders	7,700	4,100	171,700	151,600
Cash Flows Used for Investments in Plant			275,400	305,900
Assets	7,351,400		7,351,400		7,215,900
Electric Transmission | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	457,600	411,200	892,800	811,900
Depreciation and Amortization	(83,300)	(74,500)	(165,300)	(148,000)
Other Operating Expenses	(141,300)	(121,900)	(270,500)	(237,300)
Operating Income	233,000	214,800	457,000	426,600
Interest Expense	(37,500)	(32,600)	(70,600)	(65,300)
Other Income, Net	9,300	6,800	18,200	12,200
Net Income Attributable to Common Shareholders	151,500	137,600	300,000	273,000
Cash Flows Used for Investments in Plant			543,600	443,200
Assets	12,938,600		12,938,600		12,377,800
Water Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	54,600	52,800	103,100	99,200
Depreciation and Amortization	(12,500)	(11,500)	(24,800)	(22,800)
Other Operating Expenses	(27,000)	(25,400)	(54,100)	(50,500)
Operating Income	15,100	15,900	24,200	25,900
Interest Expense	(8,400)	(8,100)	(16,500)	(16,000)
Other Income, Net	2,100	900	4,200	1,900
Net Income Attributable to Common Shareholders	9,000	$ 8,900	12,700	12,600
Cash Flows Used for Investments in Plant			65,600	$ 53,800
Assets	$ 2,592,400		$ 2,592,400		$ 2,551,100