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SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2025	Apr. 30, 2025	Mar. 26, 2025	Mar. 03, 2025	Dec. 31, 2024
CL&P
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	$ 0				$ 280,000,000
CL&P | Related Party
Line of Credit Facility [Line Items]
Notes payable to Eversource parent					280,000,000.0
PSNH
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	114,500,000				131,100,000
PSNH | Related Party
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	114,500,000				131,100,000
NSTAR Gas Series R First Mortgage Bonds | NSTAR Gas Series Y First Mortgage Bonds | First Mortgage | Subsequent Event
Line of Credit Facility [Line Items]
Face amount		$ 205,000,000.0
NSTAR Gas Series R First Mortgage Bonds | NSTAR Gas Series Z First Mortgage Bonds | First Mortgage | Subsequent Event
Line of Credit Facility [Line Items]
Face amount		$ 20,000,000.0
Line of Credit | CL&P
Line of Credit Facility [Line Items]
Maximum borrowing capacity	375,000,000
Amount outstanding under line of credit	0				0
Line of Credit | PSNH
Line of Credit Facility [Line Items]
Maximum borrowing capacity	250,000,000			$ 300,000,000
Amount outstanding under line of credit	0				0
Line of Credit | Yankee Gas
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 360,000,000
Commercial Paper | NSTAR Electric
Line of Credit Facility [Line Items]
Maximum borrowing capacity	650,000,000
Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Maximum borrowing capacity	650,000,000
Eversource Parent | Commercial Paper
Line of Credit Facility [Line Items]
Maximum borrowing capacity	2,000,000,000.00
Eversource Parent | Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 2,000,000,000
Debt instrument term (in years)	5 years
NSTAR Electric | Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Debt instrument term (in years)	5 years
NSTAR Electric and Eversource | Line of Credit
Line of Credit Facility [Line Items]
Amount outstanding under line of credit	$ 0				$ 0

X

- Definition

Face (par) amount of debt instrument at time of issuance.

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X

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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X

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

Sum of the carrying values as of the balance sheet date of the portions of long-term notes payable due within one year or the operating cycle if longer.

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