SEGMENT INFORMATION - Summary of Segment Information and Segmented Total Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Operating Revenues	$ 3,795,643	$ 3,471,310
Depreciation and Amortization	(236,900)	(526,300)
Other Operating Expenses	(2,809,100)	(2,281,900)
Operating Income/(Loss)	749,573	663,055
Interest Expense	(194,543)	(153,245)
Other Income, Net	88,981	71,561
Net Income/(Loss) Attributable to Common Shareholders	491,159	443,446
Cash Flows Used for Investments in Plant	977,144	764,594
Assets	54,105,167		$ 53,230,900
Other
Segment Reporting Information [Line Items]
Operating Revenues	413,800	383,500
Depreciation and Amortization	(36,800)	(30,200)
Other Operating Expenses	(339,600)	(331,400)
Operating Income/(Loss)	37,400	21,900
Interest Expense	(85,100)	(46,800)
Other Income, Net	565,800	495,900
Net Income/(Loss) Attributable to Common Shareholders	516,900	468,700
Cash Flows Used for Investments in Plant	65,200	62,100
Assets	27,186,400		26,365,200
Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	(760,900)	(709,800)
Depreciation and Amortization	2,100	1,600
Other Operating Expenses	759,300	708,800
Operating Income/(Loss)	500	600
Interest Expense	32,000	10,100
Other Income, Net	(550,600)	(493,100)
Net Income/(Loss) Attributable to Common Shareholders	(518,100)	(482,400)
Cash Flows Used for Investments in Plant	0	0
Assets	(25,514,600)		(24,737,500)
Electric Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	2,588,600	2,386,300
Depreciation and Amortization	(22,000)	(351,600)
Other Operating Expenses	(2,342,300)	(1,845,600)
Operating Income/(Loss)	224,300	189,100
Interest Expense	(69,300)	(59,400)
Other Income, Net	54,300	47,600
Net Income/(Loss) Attributable to Common Shareholders	165,500	140,900
Cash Flows Used for Investments in Plant	371,900	280,500
Assets	27,978,800		27,365,000
Natural Gas Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	1,045,200	927,600
Depreciation and Amortization	(77,000)	(51,900)
Other Operating Expenses	(730,400)	(657,300)
Operating Income/(Loss)	237,800	218,400
Interest Expense	(21,200)	(15,800)
Other Income, Net	9,000	10,100
Net Income/(Loss) Attributable to Common Shareholders	170,300	164,000
Cash Flows Used for Investments in Plant	165,500	127,300
Assets	8,127,800		8,084,900
Electric Transmission | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	458,600	435,200
Depreciation and Amortization	(89,900)	(81,900)
Other Operating Expenses	(128,200)	(129,300)
Operating Income/(Loss)	240,500	224,000
Interest Expense	(41,500)	(33,200)
Other Income, Net	9,400	8,900
Net Income/(Loss) Attributable to Common Shareholders	155,100	148,500
Cash Flows Used for Investments in Plant	336,600	266,900
Assets	13,522,600		13,369,500
Water Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	50,300	48,500
Depreciation and Amortization	(13,300)	(12,300)
Other Operating Expenses	(27,900)	(27,100)
Operating Income/(Loss)	9,100	9,100
Interest Expense	(9,400)	(8,200)
Other Income, Net	1,100	2,200
Net Income/(Loss) Attributable to Common Shareholders	1,500	3,700
Cash Flows Used for Investments in Plant	37,900	$ 27,800
Assets	$ 2,804,200		$ 2,783,800