EMPLOYEE BENEFITS - Share-Based Payments Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted in incentive plan (up to) (in shares)	3,200,000
Shares available for issuance under incentive plan (in shares)	903,183	2,430,716
Shares outstanding (in shares)	300,592
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 81.07
Total unrecognized compensation expense	$ 24.5
Period for recognition	1 year 9 months 7 days
Tax effect on total share-based payments (in percentage)	26.00%
Excess stock benefit	$ 2.1	$ 4.0	$ 6.6
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 85.96	$ 81.89	$ 88.23
Shares outstanding (in shares)		297,270
Weighted average shares outstanding (in dollars per share)	$ 87.21	$ 83.39
Restricted stock units available (in shares)	184,540
Restricted stock unit fully vested (in shares)	329,142
Additional restricted stock unit expected to vest (in shares)	285,562
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 83.34	$ 76.08	$ 75.36
Shares outstanding (in shares)	457,069	436,957
Weighted average shares outstanding (in dollars per share)	$ 88.43	$ 81.41
Restricted stock units available (in shares)	311,553
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 73.15
Restricted stock unit fully vested (in shares)	90,221
CL&P
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 4.0
Excess stock benefit	0.7	$ 1.5	$ 2.3
NSTAR Electric
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	6.9
Excess stock benefit	0.8	1.4	2.3
PSNH
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	1.4
Excess stock benefit	$ 0.3	$ 0.5	$ 0.8
CL&P, NSTAR Electric and PSNH
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition	1 year 9 months 10 days
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

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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