EMPLOYEE BENEFITS - Schedule of Pension Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Pension and SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	$ (4,745.7)	$ (5,238.4)
Service Cost	67.9	44.3	$ 43.1
Interest Cost	255.6	250.0	254.0
Actuarial (Loss)/Gain	(190.0)	280.2
Benefits Paid	334.5	320.9
Benefits Paid - Lump Sum	28.5	24.0
Benefits Paid - SERP	18.8	19.4
Employee Transfers	(0.3)	0.0
Water Reclassified as Assets Held for Sale	0.0	142.5
Water Reclassified from Assets Held for Sale	(142.5)	0.0
Benefit Obligation as of End of Year	(5,020.2)	(4,745.7)	(5,238.4)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	5,514.0	5,775.0
Employer Contributions	2.5	5.0
Actual Return on Plan Assets	588.4	227.0
Benefits Paid - Pension	(334.5)	(320.9)
Benefits Paid - Lump Sum	(28.5)	(24.0)
Employee Transfers	0.0	0.0
Water Reclassified as Assets Held for Sale	0.0	(148.1)
Water Reclassified from Assets Held for Sale	148.1	0.0
Fair Value of Plan Assets as of End of Year	5,890.0	5,514.0	5,775.0
Funded Status as of December 31st	869.8	768.3
PBOP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(587.4)	(676.0)
Service Cost	6.4	7.0	7.6
Interest Cost	32.0	31.9	33.8
Actuarial (Loss)/Gain	(11.3)	41.3
Benefits Paid	51.7	51.7
Employee Transfers	0.0	0.0
Water Reclassified as Assets Held for Sale	0.0	34.5
Water Reclassified from Assets Held for Sale	(34.5)	0.0
Benefit Obligation as of End of Year	(619.9)	(587.4)	(676.0)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	1,036.3	1,024.4
Employer Contributions	0.7	0.9
Actual Return on Plan Assets	131.9	92.3
Benefits Paid - Pension	(51.3)	(51.8)
Employee Transfers	0.0	0.0
Water Reclassified as Assets Held for Sale	0.0	(29.5)
Water Reclassified from Assets Held for Sale	29.5	0.0
Fair Value of Plan Assets as of End of Year	1,147.1	1,036.3	1,024.4
Funded Status as of December 31st	527.2	448.9
CL&P | Pension and SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(982.9)	(1,048.5)
Service Cost	15.3	12.7	12.3
Interest Cost	51.5	50.3	50.5
Actuarial (Loss)/Gain	(37.8)	56.2
Benefits Paid	69.1	68.1
Benefits Paid - Lump Sum	0.1	0.0
Benefits Paid - SERP	0.4	0.3
Employee Transfers	1.2	4.0
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Benefit Obligation as of End of Year	(1,016.7)	(982.9)	(1,048.5)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	1,144.4	1,170.0
Employer Contributions	0.0	0.0
Actual Return on Plan Assets	119.3	46.5
Benefits Paid - Pension	(69.1)	(68.1)
Benefits Paid - Lump Sum	(0.1)	0.0
Employee Transfers	(1.2)	(4.0)
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Fair Value of Plan Assets as of End of Year	1,193.3	1,144.4	1,170.0
Funded Status as of December 31st	176.6	161.5
CL&P | PBOP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(109.1)	(120.6)
Service Cost	1.1	1.2	1.3
Interest Cost	5.6	5.6	6.2
Actuarial (Loss)/Gain	(1.6)	8.9
Benefits Paid	9.3	9.4
Employee Transfers	0.1	0.0
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Benefit Obligation as of End of Year	(108.0)	(109.1)	(120.6)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	124.4	123.0
Employer Contributions	0.0	0.0
Actual Return on Plan Assets	14.9	11.2
Benefits Paid - Pension	(9.3)	(9.4)
Employee Transfers	(0.3)	(0.4)
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Fair Value of Plan Assets as of End of Year	129.7	124.4	123.0
Funded Status as of December 31st	21.7	15.3
NSTAR Electric | Pension and SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(1,003.5)	(1,107.0)
Service Cost	9.7	7.7	7.8
Interest Cost	53.0	51.6	53.9
Actuarial (Loss)/Gain	(54.5)	74.1
Benefits Paid	67.2	67.1
Benefits Paid - Lump Sum	12.9	7.6
Benefits Paid - SERP	0.1	0.2
Employee Transfers	2.8	13.8
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Benefit Obligation as of End of Year	(1,037.7)	(1,003.5)	(1,107.0)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	1,378.2	1,411.6
Employer Contributions	0.0	0.0
Actual Return on Plan Assets	144.7	55.1
Benefits Paid - Pension	(67.2)	(67.1)
Benefits Paid - Lump Sum	(12.9)	(7.6)
Employee Transfers	(2.8)	(13.8)
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Fair Value of Plan Assets as of End of Year	1,440.0	1,378.2	1,411.6
Funded Status as of December 31st	402.3	374.7
NSTAR Electric | PBOP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(171.4)	(188.3)
Service Cost	1.1	1.2	1.2
Interest Cost	8.7	8.8	9.2
Actuarial (Loss)/Gain	(3.5)	10.7
Benefits Paid	16.0	15.9
Employee Transfers	0.0	0.3
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Benefit Obligation as of End of Year	(168.7)	(171.4)	(188.3)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	519.2	490.4
Employer Contributions	0.0	0.0
Actual Return on Plan Assets	65.0	45.8
Benefits Paid - Pension	(16.0)	(15.9)
Employee Transfers	0.6	(1.1)
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Fair Value of Plan Assets as of End of Year	568.8	519.2	490.4
Funded Status as of December 31st	400.1	347.8
PSNH | Pension and SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(521.5)	(562.3)
Service Cost	6.5	4.3	4.3
Interest Cost	27.1	26.8	27.3
Actuarial (Loss)/Gain	(11.7)	30.7
Benefits Paid	38.8	38.0
Benefits Paid - Lump Sum	1.3	0.1
Benefits Paid - SERP	0.4	0.4
Employee Transfers	0.1	2.7
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Benefit Obligation as of End of Year	(526.2)	(521.5)	(562.3)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	597.5	614.0
Employer Contributions	0.0	0.0
Actual Return on Plan Assets	61.3	24.3
Benefits Paid - Pension	(38.8)	(38.0)
Benefits Paid - Lump Sum	(1.3)	(0.1)
Employee Transfers	(0.1)	(2.7)
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Fair Value of Plan Assets as of End of Year	618.6	597.5	614.0
Funded Status as of December 31st	92.4	76.0
PSNH | PBOP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(65.9)	(72.0)
Service Cost	0.5	0.6	0.7
Interest Cost	3.4	3.4	3.7
Actuarial (Loss)/Gain	(1.2)	3.9
Benefits Paid	6.0	6.2
Employee Transfers	0.2	0.0
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Benefit Obligation as of End of Year	(64.8)	(65.9)	(72.0)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	76.4	74.7
Employer Contributions	0.0	0.0
Actual Return on Plan Assets	9.3	7.6
Benefits Paid - Pension	(5.9)	(6.1)
Employee Transfers	(0.2)	0.2
Water Reclassified as Assets Held for Sale	0.0	0.0
Water Reclassified from Assets Held for Sale	0.0	0.0
Fair Value of Plan Assets as of End of Year	79.6	76.4	$ 74.7
Funded Status as of December 31st	$ 14.8	$ 10.5