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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands, customer in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2023 USD ($) project regulatedUtility customer | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($)
Summary of Accounting Policies [Line Items] |  |  |
Number of electric and natural gas customers | customer | 4.4 |  |
Number of offshore wind projects | project | 3 |  |
Number of tax equity projects | project | 1 |  |
Goodwill | $ 4,532,100 | $ 4,522,632 | $ 4,477,300
Charitable contributions | $ 20,000 | 8,000 |
Offshore Wind Business |  |  |
Summary of Accounting Policies [Line Items] |  |  |
Ownership interest (in percent) | 50.00% |  |
Number of offshore wind projects | project | 2 |  |
Tax Equity |  |  |
Summary of Accounting Policies [Line Items] |  |  |
Ownership interest (in percent) | 50.00% |  |
Energy Relief Fund |  |  |
Summary of Accounting Policies [Line Items] |  |  |
Restricted cash, current | $ 20,000 | 20,000 |
Restricted cash, noncurrent | $ 14,100 | 15,900 |
CL&P |  |  |
Summary of Accounting Policies [Line Items] |  |  |
Period of accounts receivable recoverable under financial or medical duress | 180 days |  |
Maximum loans receivable outstanding | $ 55,000 |  |
Loans transferred receivable current | 8,500 | 9,100 |
Loans transferred receivable non-current | $ 14,500 | 13,000 |
Long term receivable |  | 25,000 |
Yankee Gas Services Company |  |  |
Summary of Accounting Policies [Line Items] |  |  |
Period of accounts receivable recoverable under financial or medical duress | 90 days |  |
NSTAR Electric |  |  |
Summary of Accounting Policies [Line Items] |  |  |
Long term receivable |  | 5,500 |
PSNH |  |  |
Summary of Accounting Policies [Line Items] |  |  |
Long term receivable |  | $ 3,800 |
Connecticut, Massachusetts and New Hampshire |  |  |
Summary of Accounting Policies [Line Items] |  |  |
Number of regulated utilities | regulatedUtility | 12 |  |

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