SEGMENT INFORMATION - Segment Information and Segmented Total Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Segment Reporting Information [Line Items]
Operating Revenues	$ 4,504,363	$ 4,118,355
Depreciation and Amortization	(823,300)	(835,000)
Total Operations and Maintenance	(506,980)	(487,451)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(2,098,000)	(1,869,500)
Operating Income	1,076,148	926,394
Interest Expense	(365,259)	(300,849)
Interest Income	28,400	34,000
Other Income, Net	72,800	58,300
Income Tax (Expense)/Benefit	(203,327)	(165,221)
Net Income	608,721	552,668
Net Income Attributable to Noncontrolling Interests	(1,880)	(1,880)
Net Income Attributable to Common Shareholders	606,841	550,788
Cash Flows Used for Investments in Plant	1,009,300	1,007,400
Assets	64,707,601		$ 63,786,711
Other
Segment Reporting Information [Line Items]
Operating Revenues	484,400	439,000
Depreciation and Amortization	(60,600)	(50,600)
Total Operations and Maintenance	(391,800)	(349,100)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(800)	(1,400)
Operating Income	31,200	37,900
Interest Expense	(180,200)	(178,400)
Interest Income	39,200	43,400
Other Income, Net	692,200	625,700
Income Tax (Expense)/Benefit	26,500	33,400
Net Income	608,900	562,000
Net Income Attributable to Noncontrolling Interests	0	0
Net Income Attributable to Common Shareholders	608,900	562,000
Cash Flows Used for Investments in Plant	85,800	50,600
Assets	30,549,200		29,743,300
Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	(931,900)	(837,800)
Depreciation and Amortization	4,100	2,800
Total Operations and Maintenance	491,100	441,000
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	436,700	394,100
Operating Income	0	100
Interest Expense	39,200	43,400
Interest Income	(39,200)	(43,400)
Other Income, Net	(687,000)	(621,100)
Income Tax (Expense)/Benefit	0	0
Net Income	(687,000)	(621,000)
Net Income Attributable to Noncontrolling Interests	0	0
Net Income Attributable to Common Shareholders	(687,000)	(621,000)
Cash Flows Used for Investments in Plant	0	0
Assets	(32,360,300)		(31,851,700)
Electric Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	2,940,500	2,777,700
Depreciation and Amortization	(541,700)	(564,700)
Operations, Excluding Storm Costs	(106,900)	(101,700)
Corporate Shared Services	(121,600)	(116,400)
Storm Costs	(28,900)	(19,900)
Employee Benefits	(39,100)	(48,600)
Uncollectible Expense	(35,600)	(43,700)
Other	(31,300)	(27,400)
Total Operations and Maintenance	(363,400)	(357,700)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(1,735,000)	(1,580,600)
Operating Income	300,400	274,700
Interest Expense	(100,000)	(91,100)
Interest Income	20,500	27,300
Other Income, Net	45,000	35,300
Income Tax (Expense)/Benefit	(61,900)	(56,600)
Net Income	204,000	189,600
Net Income Attributable to Noncontrolling Interests	(1,200)	(1,200)
Net Income Attributable to Common Shareholders	202,800	188,400
Cash Flows Used for Investments in Plant	458,900	489,600
Assets	35,382,000		34,858,100
Natural Gas Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	1,373,200	1,141,400
Depreciation and Amortization	(97,500)	(104,500)
Operations, Excluding Storm Costs	(50,700)	(46,200)
Corporate Shared Services	(30,400)	(30,300)
Storm Costs	0	0
Employee Benefits	(20,900)	(18,600)
Uncollectible Expense	(33,500)	(30,000)
Other	(300)	2,100
Total Operations and Maintenance	(135,800)	(123,000)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(717,900)	(605,200)
Operating Income	422,000	308,700
Interest Expense	(34,000)	(28,400)
Interest Income	7,800	6,700
Other Income, Net	6,700	5,500
Income Tax (Expense)/Benefit	(107,200)	(74,100)
Net Income	295,300	218,400
Net Income Attributable to Noncontrolling Interests	0	0
Net Income Attributable to Common Shareholders	295,300	218,400
Cash Flows Used for Investments in Plant	152,100	193,900
Assets	10,919,000		10,865,500
Electric Transmission | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	584,600	547,800
Depreciation and Amortization	(115,200)	(106,800)
Operations, Excluding Storm Costs	(34,700)	(31,500)
Corporate Shared Services	(21,700)	(21,800)
Storm Costs	0	0
Employee Benefits	(11,700)	(11,700)
Uncollectible Expense	0	0
Other	(16,300)	(10,900)
Total Operations and Maintenance	(84,400)	(75,900)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(74,100)	(69,600)
Operating Income	310,900	295,500
Interest Expense	(83,100)	(38,600)
Interest Income	100	0
Other Income, Net	14,200	12,100
Income Tax (Expense)/Benefit	(61,000)	(68,900)
Net Income	181,100	200,100
Net Income Attributable to Noncontrolling Interests	(700)	(700)
Net Income Attributable to Common Shareholders	180,400	199,400
Cash Flows Used for Investments in Plant	281,700	244,800
Assets	17,227,400		17,193,900
Water Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	53,600	50,300
Depreciation and Amortization	(12,400)	(11,200)
Total Operations and Maintenance	(22,700)	(22,800)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(6,900)	(6,800)
Operating Income	11,600	9,500
Interest Expense	(7,200)	(7,700)
Interest Income	0	0
Other Income, Net	1,700	800
Income Tax (Expense)/Benefit	300	1,000
Net Income	6,400	3,600
Net Income Attributable to Noncontrolling Interests	0	0
Net Income Attributable to Common Shareholders	6,400	3,600
Cash Flows Used for Investments in Plant	30,800	$ 28,500
Assets	$ 2,990,300		$ 2,977,600