EMPLOYEE BENEFITS - Share-Based Payments Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted in incentive plan (up to) (in shares)	7,400,000
Shares available for issuance under incentive plan (in shares)	3,051,466	3,790,353
Shares outstanding (in shares)	534,754
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 68.77
Total unrecognized compensation expense	$ 30.9
Period for recognition	1 year 9 months
Tax effect on total share-based payments (in percentage)	26.00%
Tax deficiency/(excess stock benefit)	$ (2.8)	$ (2.3)	$ (0.5)
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 57.63	$ 57.93	$ 76.42
Shares outstanding (in shares)		455,620
Weighted average shares outstanding (in dollars per share)	$ 59.50	$ 65.29
Restricted stock units available (in shares)	239,469
Restricted stock unit fully vested (in shares)	196,427
Additional restricted stock unit expected to vest (in shares)	508,017
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 57.82	$ 55.87	$ 83.39
Shares outstanding (in shares)	941,243	737,738
Weighted average shares outstanding (in dollars per share)	$ 61.77	$ 69.12
Restricted stock units available (in shares)	113,252
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 77.29
Restricted stock unit fully vested (in shares)	77,200
CL&P
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 5.3
Period for recognition	1 year 9 months
Tax deficiency/(excess stock benefit)		$ (0.8)	$ (0.2)
NSTAR Electric
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 9.5
Period for recognition	1 year 9 months
Tax deficiency/(excess stock benefit)		(0.8)	(0.2)
PSNH
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 1.9
Period for recognition	1 year 9 months
Tax deficiency/(excess stock benefit)		$ (0.3)	$ (0.1)
Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of graded vesting schedule under long-term incentive program	3 years
Board Members
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of graded vesting schedule under long-term incentive program	1 year