SEGMENT INFORMATION - Summary of Segment Information and Segmented Total Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Operating Revenues	$ 3,471,310	$ 2,825,840
Depreciation and Amortization	(526,300)	(378,700)
Other Operating Expenses	(2,281,900)	(1,861,500)
Operating Income/(Loss)	663,055	585,568
Interest Expense	(153,245)	(137,766)
Other Income, Net	71,561	34,201
Net Income/(Loss) Attributable to Common Shareholders	443,446	366,143
Cash Flows Used for Investments in Plant	764,594	688,983
Assets	49,289,152		$ 48,492,144
Other
Segment Reporting Information [Line Items]
Operating Revenues	383,500	343,000
Depreciation and Amortization	(30,200)	(27,300)
Other Operating Expenses	(331,400)	(299,500)
Operating Income/(Loss)	21,900	16,200
Interest Expense	(46,800)	(41,600)
Other Income, Net	495,900	424,100
Net Income/(Loss) Attributable to Common Shareholders	468,700	394,900
Cash Flows Used for Investments in Plant	62,100	47,800
Assets	23,394,300		22,674,700
Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	(709,800)	(645,000)
Depreciation and Amortization	1,600	1,000
Other Operating Expenses	708,800	644,800
Operating Income/(Loss)	600	800
Interest Expense	10,100	11,600
Other Income, Net	(493,100)	(421,000)
Net Income/(Loss) Attributable to Common Shareholders	(482,400)	(408,600)
Cash Flows Used for Investments in Plant	0	0
Assets	(22,647,900)		(21,738,600)
Electric Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	2,386,300	1,900,300
Depreciation and Amortization	(351,600)	(221,900)
Other Operating Expenses	(1,845,600)	(1,530,500)
Operating Income/(Loss)	189,100	147,900
Interest Expense	(59,400)	(53,300)
Other Income, Net	47,600	20,700
Net Income/(Loss) Attributable to Common Shareholders	140,900	93,200
Cash Flows Used for Investments in Plant	280,500	256,600
Assets	25,883,200		25,411,200
Natural Gas Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	927,600	780,500
Depreciation and Amortization	(51,900)	(45,700)
Other Operating Expenses	(657,300)	(535,800)
Operating Income/(Loss)	218,400	199,000
Interest Expense	(15,800)	(13,900)
Other Income, Net	10,100	3,900
Net Income/(Loss) Attributable to Common Shareholders	164,000	147,600
Cash Flows Used for Investments in Plant	127,300	131,800
Assets	7,329,700		7,215,900
Electric Transmission | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	435,200	400,600
Depreciation and Amortization	(81,900)	(73,500)
Other Operating Expenses	(129,300)	(115,400)
Operating Income/(Loss)	224,000	211,700
Interest Expense	(33,200)	(32,700)
Other Income, Net	8,900	5,500
Net Income/(Loss) Attributable to Common Shareholders	148,500	135,400
Cash Flows Used for Investments in Plant	266,900	225,200
Assets	12,757,800		12,377,800
Water Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	48,500	46,400
Depreciation and Amortization	(12,300)	(11,300)
Other Operating Expenses	(27,100)	(25,100)
Operating Income/(Loss)	9,100	10,000
Interest Expense	(8,200)	(7,900)
Other Income, Net	2,200	1,000
Net Income/(Loss) Attributable to Common Shareholders	3,700	3,600
Cash Flows Used for Investments in Plant	27,800	$ 27,600
Assets	$ 2,572,100		$ 2,551,100