INCOME TAXES - Reconciliation Between Income Tax Expense and Expected Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax Contingency [Line Items]
Income/(Loss) Before Income Tax Benefit	$ 1,840,177	$ 1,243,836	$ (275,037)
Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract]
Statutory Federal Income Tax Expense at 21%	386,400	261,200	(57,700)
State Income Taxes, Net of Federal Impact	2,400	43,200	(11,400)
Research and Development Tax Credits	(22,600)
Tax Asset Valuation   Allowance/Reserve Adjustments	(241,600)	278,600	295,800
Depreciation	(23,400)	(22,600)	(25,800)
EDIT Amortization	(50,600)	(37,000)	(51,500)
Other Federal Tax Credits		(67,000)	(42,500)
Dividends on ESOP		(5,500)	(5,300)
Share-Based Payment Tax Deficiency	2,800	2,300	500
Loss on Offshore Wind	59,500
Other, Net	30,200	(26,400)	59,700
Income Tax Expense	$ 140,286	$ 424,664	$ 159,684
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal Statutory Income Tax Expense at 21%	21.00%
State and Local Income Tax Effects, Net of Federal Impact	0.10%
Research and Development Tax Credits	(1.20%)
Changes in Valuation Allowances	(13.10%)
Depreciation	(1.30%)
EDIT Amortization	(2.70%)
Loss on Offshore Wind	3.20%
Other	1.60%
Effective Income Tax Rate Reconciliation, Percent	7.60%	34.10%	(58.10%)
CL&P
Income Tax Contingency [Line Items]
Income/(Loss) Before Income Tax Benefit	$ 718,532	$ 707,057	$ 689,642
Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract]
Statutory Federal Income Tax Expense at 21%	150,900	148,500	144,900
State Income Taxes, Net of Federal Impact	39,600	(2,800)	(10,700)
Research and Development Tax Credits	0
Tax Asset Valuation   Allowance/Reserve Adjustments	(6,200)	50,800	51,300
Depreciation	2,500	400	(5,600)
EDIT Amortization	(17,000)	(9,200)	(10,500)
Investment Tax Credit Amortization	0	0	0
Other Federal Tax Credits		0	0
Dividends on ESOP		0	0
Share-Based Payment Tax Deficiency		800	200
Loss on Offshore Wind	0
Other, Net	(2,600)	6,000	1,300
Income Tax Expense	$ 167,203	$ 194,459	$ 170,909
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal Statutory Income Tax Expense at 21%	21.00%
State and Local Income Tax Effects, Net of Federal Impact	5.50%
Research and Development Tax Credits	0.00%
Changes in Valuation Allowances	(0.90%)
Depreciation	0.30%
EDIT Amortization	(2.40%)
Loss on Offshore Wind	0.00%
Other	(0.40%)
Effective Income Tax Rate Reconciliation, Percent	23.30%	27.50%	24.80%
NSTAR Electric
Income Tax Contingency [Line Items]
Income/(Loss) Before Income Tax Benefit	$ 820,653	$ 826,929	$ 697,524
Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract]
Statutory Federal Income Tax Expense at 21%	172,300	173,700	146,500
State Income Taxes, Net of Federal Impact	49,600	49,400	42,500
Research and Development Tax Credits	0
Tax Asset Valuation   Allowance/Reserve Adjustments	0	0	0
Depreciation	(10,600)	(10,900)	(8,800)
EDIT Amortization	(21,700)	(20,000)	(28,400)
Investment Tax Credit Amortization	(1,700)	(1,700)	(1,700)
Other Federal Tax Credits		0	0
Dividends on ESOP		0	0
Share-Based Payment Tax Deficiency		800	200
Loss on Offshore Wind	0
Other, Net	400	(700)	2,700
Income Tax Expense	$ 190,030	$ 190,576	$ 152,996
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal Statutory Income Tax Expense at 21%	21.00%
State and Local Income Tax Effects, Net of Federal Impact	6.00%
Research and Development Tax Credits	0.00%
Changes in Valuation Allowances	0.00%
Depreciation	(1.30%)
EDIT Amortization	(2.60%)
Loss on Offshore Wind	0.00%
Other	0.00%
Effective Income Tax Rate Reconciliation, Percent	23.20%	23.00%	21.90%
PSNH
Income Tax Contingency [Line Items]
Income/(Loss) Before Income Tax Benefit	$ 361,500	$ 285,128	$ 254,673
Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract]
Statutory Federal Income Tax Expense at 21%	75,900	59,900	53,500
State Income Taxes, Net of Federal Impact	24,600	16,700	14,100
Research and Development Tax Credits	0
Tax Asset Valuation   Allowance/Reserve Adjustments	0	0	0
Depreciation	(2,200)	(1,000)	(1,000)
EDIT Amortization	(8,100)	(6,500)	(6,800)
Investment Tax Credit Amortization	0	0	0
Other Federal Tax Credits		0	0
Dividends on ESOP		0	0
Share-Based Payment Tax Deficiency		300	100
Loss on Offshore Wind	0
Other, Net	1,900	800	(900)
Income Tax Expense	$ 92,146	$ 70,245	$ 59,014
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal Statutory Income Tax Expense at 21%	21.00%
State and Local Income Tax Effects, Net of Federal Impact	6.80%
Research and Development Tax Credits	0.00%
Changes in Valuation Allowances	0.00%
Depreciation	(0.60%)
EDIT Amortization	(2.20%)
Loss on Offshore Wind	0.00%
Other	0.50%
Effective Income Tax Rate Reconciliation, Percent	25.50%	24.60%	23.20%