SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Summary of Accounting Policies [Line Items]
Other Income, Net	$ 346,088	$ 161,282	$ 108,590
Unrealized gain associated with investment	22,900	14,200	14,200
Renewable Energy Fund
Summary of Accounting Policies [Line Items]
Other-than-temporary impairment		2,800	2,800
Pension, SERP and PBOP Non-Service Income Components, Net of Deferred Portion
Summary of Accounting Policies [Line Items]
Other Income, Net	219,800	84,400	44,400
AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	47,300	37,300	42,000
Equity in Earnings of Unconsolidated Affiliates
Summary of Accounting Policies [Line Items]
Other Income, Net	22,900	14,200	14,200
Unrealized gain associated with investment	12,200	2,100	2,400
Investment (Loss)/Income
Summary of Accounting Policies [Line Items]
Other Income, Net	1,900	(200)	1,100
Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	50,500	25,600	4,800
Other
Summary of Accounting Policies [Line Items]
Other Income, Net	1,100	(100)	300
Gain on Sale of Property
Summary of Accounting Policies [Line Items]
Other Income, Net	2,600	100	1,800
CL&P
Summary of Accounting Policies [Line Items]
Other Income, Net	83,252	30,187	20,774
CL&P | Pension, SERP and PBOP Non-Service Income Components, Net of Deferred Portion
Summary of Accounting Policies [Line Items]
Other Income, Net	64,400	15,200	3,800
CL&P | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	13,600	7,700	13,800
CL&P | Investment (Loss)/Income
Summary of Accounting Policies [Line Items]
Other Income, Net	(1,300)	1,300	1,100
CL&P | Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	6,500	5,900	2,000
CL&P | Other
Summary of Accounting Policies [Line Items]
Other Income, Net	100	100	100
NSTAR Electric
Summary of Accounting Policies [Line Items]
Other Income, Net	142,661	74,844	52,017
NSTAR Electric | Pension, SERP and PBOP Non-Service Income Components, Net of Deferred Portion
Summary of Accounting Policies [Line Items]
Other Income, Net	85,500	40,200	29,300
NSTAR Electric | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	24,600	20,400	21,500
NSTAR Electric | Investment (Loss)/Income
Summary of Accounting Policies [Line Items]
Other Income, Net	1,200	100	(800)
NSTAR Electric | Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	30,700	13,400	900
NSTAR Electric | Other
Summary of Accounting Policies [Line Items]
Other Income, Net	700	700	1,100
PSNH
Summary of Accounting Policies [Line Items]
Other Income, Net	32,666	14,565	13,786
PSNH | Pension, SERP and PBOP Non-Service Income Components, Net of Deferred Portion
Summary of Accounting Policies [Line Items]
Other Income, Net	26,800	10,300	7,000
PSNH | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	2,500	1,600	4,200
PSNH | Investment (Loss)/Income
Summary of Accounting Policies [Line Items]
Other Income, Net	200	100	100
PSNH | Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	3,100	2,400	2,400
PSNH | Other
Summary of Accounting Policies [Line Items]
Other Income, Net	$ 100	$ 200	$ 100