REGULATORY ACCOUNTING - Narrative (Details)			4 Months Ended	12 Months Ended
	Jan. 01, 2023 USD ($)	Nov. 01, 2022 USD ($)	Apr. 30, 2023 USD ($)	Dec. 31, 2022 USD ($) storm	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2022 USD ($)	Oct. 01, 2021 USD ($)	May 06, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2019 USD ($)	May 31, 2018 USD ($)
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				$ 210,800,000	$ 252,500,000
Deferred costs related to uncollectible expense				29,800,000	33,000,000
Regulatory Liabilities				890,786,000	602,432,000
Gain (loss) related to litigation settlement				72,041,000	(81,274,000)	$ 0
Regulatory assets				5,578,300,000	5,715,800,000
Increase (decrease) in regulatory assets				205,294,000	314,211,000	516,411,000
Cash, Cash Equivalents and Restricted Cash as reported on the Statements of Cash Flows				521,752,000	221,008,000	264,950,000					$ 117,063,000
FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers				39,100,000
Unfavorable Regulatory Action
Regulatory Assets [Line Items]
Gain (loss) related to litigation settlement				(103,600,000)
Unfavorable Regulatory Action | Oil and Gas, Operation and Maintenance
Regulatory Assets [Line Items]
Gain (loss) related to litigation settlement				(10,000,000)
Deferred Pre-Staging And Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				399,000,000
Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				$ 1,400,000,000
Goodwill-related
Regulatory Assets [Line Items]
Recovery period (in years)				40 years
Remaining amortization (in years)				17 years
Regulatory assets				$ 281,000,000.0	297,800,000
Storm Costs, Net
Regulatory Assets [Line Items]
Regulatory assets				1,379,100,000	1,102,700,000
PSNH
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				1,000,000	3,400,000
Equity return not recorded on the balance sheet				4,100,000	5,000,000
Regulatory Liabilities				161,963,000	120,176,000
Regulatory assets				696,200,000	786,400,000
Increase (decrease) in regulatory assets				(53,181,000)	(32,587,000)	45,830,000
Cash, Cash Equivalents and Restricted Cash as reported on the Statements of Cash Flows				36,812,000	35,126,000	39,555,000					36,688,000
PSNH | FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers				3,100,000
PSNH | Deferred Pre-Staging And Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				55,000,000
PSNH | Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				98,000,000
PSNH | Goodwill-related
Regulatory Assets [Line Items]
Regulatory assets				0	0
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Regulatory assets				95,400,000	65,800,000
CL&P
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				135,900,000	114,900,000
Deferred costs related to uncollectible expense				11,800,000	18,000,000
Regulatory Liabilities				336,048,000	266,489,000
Gain (loss) related to litigation settlement				72,041,000	(81,274,000)	0
Regulatory assets				1,907,800,000	2,084,800,000
Increase (decrease) in regulatory assets				144,793,000	152,775,000	279,941,000
Cash, Cash Equivalents and Restricted Cash as reported on the Statements of Cash Flows				20,327,000	74,788,000	99,809,000					4,971,000
CL&P | Energy Assistance Program
Regulatory Assets [Line Items]
Restricted cash				10,000,000
CL&P | Customer Assistance Fund
Regulatory Assets [Line Items]
Cash, Cash Equivalents and Restricted Cash as reported on the Statements of Cash Flows							$ 10,000,000
CL&P | Forecast
Regulatory Assets [Line Items]
Average monthly bill			$ 10
Public utilities, approved rate increase (decrease), net revenues generated			$ 90,000,000
CL&P | FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers				21,400,000
CL&P | Unfavorable Regulatory Action
Regulatory Assets [Line Items]
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards									$ 28,400,000	$ 28,400,000
Period credits are issued to customers (in years)									1 year
Regulatory Liabilities				75,000,000	75,000,000
Customer credits								$ 65,000,000
Customer assistance initiatives								$ 10,000,000
CL&P | Unfavorable Regulatory Action | Oil and Gas, Operation and Maintenance
Regulatory Assets [Line Items]
Gain (loss) related to litigation settlement				(10,000,000)
CL&P | Deferred Pre-Staging And Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				163,000,000
CL&P | Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				807,000,000
CL&P | Deferred Storm Restoration Costs | Tropical Storm Isaias
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				235,000,000
CL&P | Goodwill-related
Regulatory Assets [Line Items]
Regulatory assets				0	0
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Regulatory assets				799,300,000	695,600,000
NSTAR Electric
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				19,800,000	85,000,000
Deferred costs related to uncollectible expense				2,200,000	6,100,000
Regulatory Liabilities				$ 373,221,000	228,248,000
Renewal term of performance-based ratemaking plan (in years)				5 years
Extension period (in years)				5 years
Historical average term of capital additions (in years)				5 years
Authorized regulatory ROE (in percent)				9.80%
Authorized common equity ratio (in percent)				53.20%
Regulatory assets				$ 1,714,400,000	1,579,200,000
Increase (decrease) in regulatory assets				$ 88,220,000	79,075,000	186,081,000
Storms in a calendar year | storm				8
Storms recovered at base rate | storm				6
Number of additional storms | storm				2
Cash, Cash Equivalents and Restricted Cash as reported on the Statements of Cash Flows				$ 345,293,000	18,179,000	$ 17,410,000					$ 6,312,000
NSTAR Electric | Subsequent Event
Regulatory Assets [Line Items]
Rate increase approved	$ 64,000,000
NSTAR Electric | FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers				14,600,000
NSTAR Electric | Deferred Pre-Staging And Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				181,000,000
NSTAR Electric | Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved				492,000,000
NSTAR Electric | Goodwill-related
Regulatory Assets [Line Items]
Regulatory assets				241,200,000	255,700,000
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Regulatory assets				484,400,000	$ 341,300,000
NSTAR Electric | Storm Fund Contribution
Regulatory Assets [Line Items]
Regulatory assets				10,000,000
Increase (decrease) in regulatory assets				31,000,000
NSTAR Electric | Storm Threshold Costs
Regulatory Assets [Line Items]
Regulatory assets				1,300,000
NSTAR Electric | Recovery of Storm Costs | Subsequent Event
Regulatory Assets [Line Items]
Regulatory assets	$ 162,100,000
Recovery period of regulatory asset (in years)	5 years
NSTAR Electric | Recovery of exogenous storms
Regulatory Assets [Line Items]
Regulatory assets				$ 220,900,000
Recovery period of regulatory asset (in years)				5 years
NSTAR Electric | Recovery of historical exogenous property taxes from 2020 - 2022 | Subsequent Event
Regulatory Assets [Line Items]
Regulatory assets	$ 30,800,000
Recovery period of regulatory asset (in years)	2 years
NSTAR Electric | Recovery of historical exogenous property taxes from 2012 - 2015 | Subsequent Event
Regulatory Assets [Line Items]
Regulatory assets	$ 8,300,000
Recovery period of regulatory asset (in years)	5 years
NSTAR Gas
Regulatory Assets [Line Items]
Rate increase approved		$ 21,700,000
NSTAR Gas | Exogenous Property Taxes
Regulatory Assets [Line Items]
Rate increase approved		4,500,000
NSTAR Gas | Mitigation Plan
Regulatory Assets [Line Items]
Rate increase approved		5,400,000
NSTAR Gas | Recovery of Exogenous Property Taxes
Regulatory Assets [Line Items]
Regulatory assets		$ 8,200,000
Recovery period of regulatory asset (in years)		2 years
EGMA
Regulatory Assets [Line Items]
Rate increase approved		$ 6,700,000
EGMA | Tax Act Credit Factor
Regulatory Assets [Line Items]
Rate increase approved		3,300,000
EGMA | Recovery of Exogenous Property Taxes
Regulatory Assets [Line Items]
Regulatory assets		$ 8,600,000
Recovery period of regulatory asset (in years)		2 years
Rate Reduction Bonds | PSNH
Regulatory Assets [Line Items]
Amount of securitized rate reduction bonds issued												$ 635,700,000