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SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($) | 9 Months Ended |  |  |
--- | --- | --- | --- | ---
Sep. 30, 2021 | Sep. 10, 2021 | Mar. 31, 2021 | Dec. 31, 2020
NSTAR Electric |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Long-term Line of Credit, Noncurrent | $ 80,000,000 |  |  |
Notes payable to Eversource parent | 24,600,000 |  |  | $ 21,300,000
Amount of long-term debt requested for issuance |  |  | $ 1,600,000,000 |
PSNH |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Notes payable to Eversource parent | 66,500,000 |  |  | 46,300,000
Massachusetts Department of Public Utilities |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Amount of long-term debt requested for issuance |  | $ 725,000,000 |  |
Line of Credit | CL&P |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Maximum borrowing capacity | 450,000,000 |  |  |
Amount outstanding under line of credit | 0 |  |  |
Line of Credit | PSNH |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Maximum borrowing capacity | 300,000,000 |  |  |
Amount outstanding under line of credit | 0 |  |  |
Commercial Paper | NSTAR Electric |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Maximum borrowing capacity | 650,000,000 |  |  |
Line of Credit |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Amount outstanding under line of credit | 0 |  |  | $ 0
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 |  |  |
Eversource Parent | Line of Credit |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Maximum borrowing capacity | $ 2,000,000,000 |  |  |
Debt instrument term | 5 years |  |  |
NSTAR Electric | Line of Credit | NSTAR Electric |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Debt instrument term | 5 years |  |  |

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- 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 + Details
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- Definition The carrying value as of the balance sheet date of the noncurrent portion 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=99376301&loc=d3e1336-112600 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 45 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=99376301&loc=d3e1314-112600 + Details
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