SEGMENT INFORMATION - Schedule of Segment Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Revenues	$ 13,547,244	$ 11,900,809	$ 11,910,705
Depreciation and Amortization	(2,404,500)	(1,776,400)	(815,700)
Operations, Excluding Storm Costs
Corporate Shared Services, (General and Administrative)
Storm Costs
Employee Benefits
Uncollectible Expense
Operations and Maintenance	(2,073,778)	(2,012,926)	(1,895,703)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(6,080,300)	(5,405,800)	(6,800,000)
Loss on Pending Sale of Aquarion	0	(297,000)	0
Operating Income	2,988,589	2,408,709	2,399,335
Interest Expense	(1,243,266)	(1,111,336)	(855,441)
Loss on Offshore Wind	(284,000)	(464,019)	(2,167,000)
Interest Income	125,500	138,200	94,200
Other Income, Net	253,400	272,300	253,900
Income Tax (Expense)/Benefit	(140,286)	(424,664)	(159,684)
Net Income/(Loss)	1,699,891	819,172	(434,721)
Net Income Attributable to Noncontrolling Interests	(7,519)	(7,519)	(7,519)
Net Income/(Loss) Attributable to Common Shareholders	1,692,372	811,653	(442,240)
Total Assets (as of)	63,786,711	59,594,529
Cash Flows Used for Investments in Plant	4,158,700	4,480,500	4,336,800
CL&P
Segment Reporting Information [Line Items]
Revenues	5,240,994	4,614,977	4,578,804
Operations and Maintenance	(848,979)	(815,345)	(733,287)
Operating Income	870,652	860,470	821,443
Interest Expense	(211,856)	(231,004)	(193,361)
Income Tax (Expense)/Benefit	(167,203)	(194,459)	(170,909)
Total Assets (as of)	17,178,739	16,839,845
NSTAR Electric
Segment Reporting Information [Line Items]
Revenues	3,986,599	3,720,877	3,515,539
Operations and Maintenance	(792,319)	(735,019)	(668,466)
Operating Income	884,068	858,318	722,649
Interest Expense	(256,061)	(222,794)	(189,254)
Income Tax (Expense)/Benefit	(190,030)	(190,576)	(152,996)
Total Assets (as of)	20,532,899	18,075,248
PSNH
Segment Reporting Information [Line Items]
Revenues	1,376,351	1,294,493	1,447,873
Operations and Maintenance	(299,170)	(288,342)	(284,442)
Operating Income	408,472	331,775	300,862
Interest Expense	(89,960)	(77,770)	(72,786)
Income Tax (Expense)/Benefit	(92,146)	(70,245)	(59,014)
Total Assets (as of)	7,029,231	6,641,941
Operating Segments | Electric Distribution
Segment Reporting Information [Line Items]
Revenues	10,039,600	9,066,500	8,973,500
Depreciation and Amortization	(1,435,100)	(934,700)	(18,200)
Operations, Excluding Storm Costs	(432,800)	(447,300)	(418,200)
Corporate Shared Services, (General and Administrative)	(443,400)	(457,100)	(397,200)
Storm Costs	(89,200)	(76,800)	(71,100)
Employee Benefits	(266,600)	(202,500)	(175,600)
Uncollectible Expense	(167,200)	(182,800)	(161,900)
Other	(170,800)	(135,900)	(167,900)
Operations and Maintenance	(1,570,000)	(1,502,400)	(1,391,900)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(6,048,000)	(5,685,300)	(6,712,700)
Loss on Pending Sale of Aquarion		0
Operating Income	986,500	944,100	850,700
Interest Expense	(386,300)	(359,100)	(291,700)
Loss on Offshore Wind	0	0	0
Interest Income	98,200	114,600	74,500
Other Income, Net	155,900	134,700	136,200
Income Tax (Expense)/Benefit	(182,600)	(198,000)	(157,100)
Net Income/(Loss)	671,700	636,300	612,600
Net Income Attributable to Noncontrolling Interests	(4,600)	(4,600)	(4,600)
Net Income/(Loss) Attributable to Common Shareholders	667,100	631,700	608,000
Total Assets (as of)	34,858,100	32,031,900
Cash Flows Used for Investments in Plant	1,872,600	1,807,400	1,668,100
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Revenues	2,634,800	2,103,900	2,221,700
Depreciation and Amortization	(279,700)	(216,600)	(214,200)
Operations, Excluding Storm Costs	(181,500)	(180,900)	(172,800)
Corporate Shared Services, (General and Administrative)	(114,200)	(106,100)	(103,000)
Storm Costs	0	0	0
Employee Benefits	(89,300)	(76,900)	(76,600)
Uncollectible Expense	(74,300)	(48,400)	(64,800)
Other	(46,600)	(29,200)	(27,500)
Operations and Maintenance	(505,900)	(441,500)	(444,700)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(1,314,400)	(1,007,100)	(1,217,900)
Loss on Pending Sale of Aquarion		0
Operating Income	534,800	438,700	344,900
Interest Expense	(119,400)	(99,200)	(85,700)
Loss on Offshore Wind	0	0	0
Interest Income	26,800	23,200	18,200
Other Income, Net	30,500	22,400	20,400
Income Tax (Expense)/Benefit	(112,200)	(94,100)	(73,000)
Net Income/(Loss)	360,500	291,000	224,800
Net Income Attributable to Noncontrolling Interests	0	0	0
Net Income/(Loss) Attributable to Common Shareholders	360,500	291,000	224,800
Total Assets (as of)	10,865,500	9,786,700
Cash Flows Used for Investments in Plant	834,600	934,500	844,100
Operating Segments | Electric Transmission
Segment Reporting Information [Line Items]
Revenues	2,283,300	2,121,000	1,915,900
Depreciation and Amortization	(437,100)	(405,100)	(371,200)
Operations, Excluding Storm Costs	(152,000)	(135,100)	(124,700)
Corporate Shared Services, (General and Administrative)	(77,000)	(74,600)	(62,500)
Storm Costs	0	0	(1,300)
Employee Benefits	(58,600)	(52,700)	(46,100)
Uncollectible Expense	0	0	0
Other	(79,700)	(71,100)	(57,400)
Operations and Maintenance	(367,300)	(333,500)	(292,000)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(302,200)	(276,000)	(258,500)
Loss on Pending Sale of Aquarion		0
Operating Income	1,176,700	1,106,400	994,200
Interest Expense	(171,600)	(172,400)	(163,700)
Loss on Offshore Wind	0	0	0
Interest Income	400	300	400
Other Income, Net	40,900	50,500	41,200
Income Tax (Expense)/Benefit	(266,800)	(257,300)	(225,800)
Net Income/(Loss)	779,600	727,500	646,300
Net Income Attributable to Noncontrolling Interests	(2,900)	(2,900)	(2,900)
Net Income/(Loss) Attributable to Common Shareholders	776,700	724,600	643,400
Total Assets (as of)	17,193,900	16,070,900
Cash Flows Used for Investments in Plant	1,094,000	1,343,300	1,406,300
Operating Segments | Water Distribution
Segment Reporting Information [Line Items]
Revenues	236,900	229,300	232,500
Depreciation and Amortization	(46,800)	(32,300)	(56,000)
Operations, Excluding Storm Costs
Corporate Shared Services, (General and Administrative)
Storm Costs
Employee Benefits
Uncollectible Expense
Operations and Maintenance	(95,600)	(98,700)	(93,200)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(27,400)	(26,300)	(23,900)
Loss on Pending Sale of Aquarion		(297,000)
Operating Income	67,100	(225,000)	59,400
Interest Expense	(30,800)	(36,200)	(38,500)
Loss on Offshore Wind	0	0	0
Interest Income	100	100	0
Other Income, Net	6,100	7,200	5,900
Income Tax (Expense)/Benefit	1,700	200	6,300
Net Income/(Loss)	44,200	(253,700)	33,100
Net Income Attributable to Noncontrolling Interests	0	0	0
Net Income/(Loss) Attributable to Common Shareholders	44,200	(253,700)	33,100
Total Assets (as of)	2,977,600	2,515,800
Cash Flows Used for Investments in Plant	165,300	161,800	167,000
Other
Segment Reporting Information [Line Items]
Revenues	1,732,700	1,701,300	1,636,600
Depreciation and Amortization	(220,100)	(198,700)	(158,800)
Operations, Excluding Storm Costs
Corporate Shared Services, (General and Administrative)
Storm Costs
Employee Benefits
Uncollectible Expense
Operations and Maintenance	(1,285,200)	(1,350,500)	(1,325,600)
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	(3,900)	(7,600)	(4,200)
Loss on Pending Sale of Aquarion		0
Operating Income	223,500	144,500	148,000
Interest Expense	(701,200)	(662,700)	(425,300)
Loss on Offshore Wind	(284,000)	(464,000)	(2,167,000)
Interest Income	166,000	218,300	150,600
Other Income, Net	1,943,500	1,416,900	(261,800)
Income Tax (Expense)/Benefit	419,600	124,500	289,900
Net Income/(Loss)	1,767,400	777,500	(2,265,600)
Net Income Attributable to Noncontrolling Interests	0	0	0
Net Income/(Loss) Attributable to Common Shareholders	1,767,400	777,500	(2,265,600)
Total Assets (as of)	29,743,300	29,041,100
Cash Flows Used for Investments in Plant	192,200	233,500	251,300
Eliminations
Segment Reporting Information [Line Items]
Revenues	(3,380,100)	(3,321,200)	(3,069,500)
Depreciation and Amortization	14,300	11,000	2,700
Operations, Excluding Storm Costs
Corporate Shared Services, (General and Administrative)
Storm Costs
Employee Benefits
Uncollectible Expense
Operations and Maintenance	1,750,200	1,713,700	1,651,700
Purchased Power, Purchased Natural Gas and Transmission, Other Taxes and Energy Efficiency	1,615,600	1,596,500	1,417,200
Loss on Pending Sale of Aquarion		0
Operating Income	0	0	2,100
Interest Expense	166,000	218,300	149,500
Loss on Offshore Wind	0	0	0
Interest Income	(166,000)	(218,300)	(149,500)
Other Income, Net	(1,923,500)	(1,359,400)	312,000
Income Tax (Expense)/Benefit	0	0	0
Net Income/(Loss)	(1,923,500)	(1,359,400)	314,100
Net Income Attributable to Noncontrolling Interests	0	0	0
Net Income/(Loss) Attributable to Common Shareholders	(1,923,500)	(1,359,400)	314,100
Total Assets (as of)	(31,851,700)	(29,851,900)
Cash Flows Used for Investments in Plant	$ 0	$ 0	$ 0