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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2025 USD ($) regulatedUtility customer | Dec. 31, 2024 USD ($)
Summary of Accounting Policies [Line Items] |  |
Number of electric, natural gas and water customers | customer | 4,600,000 |
Energy Relief Fund - Merrimack Valley Programs |  |
Summary of Accounting Policies [Line Items] |  |
Restricted cash, current | $ 20.0 | $ 20.0
Restricted cash, noncurrent | $ 6.1 | $ 5.9
CL&P |  |
Summary of Accounting Policies [Line Items] |  |
Period of accounts receivable recoverable under financial or medical duress | 180 days |
Yankee Gas |  |
Summary of Accounting Policies [Line Items] |  |
Period of accounts receivable recoverable under financial or medical duress | 90 days |
Connecticut, Massachusetts and New Hampshire |  |
Summary of Accounting Policies [Line Items] |  |
Number of regulated utilities | regulatedUtility | 12 |

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