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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) customer in Millions |  | 3 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Mar. 21, 2023 USD ($) | Mar. 31, 2023 USD ($) regulatedUtility project customer | Dec. 31, 2022 USD ($) | May 04, 2022 | Mar. 31, 2022 USD ($) | Dec. 31, 2021 USD ($)
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Number of electric, natural gas and water customers | customer |  | 4.4 |  |  |  |
Allowance for uncollectible accounts for late fees and other receivable amounts |  | $ 535,100,000 | $ 486,300,000 |  | $ 432,200,000 | $ 417,400,000
Number of offshore wind projects | project |  | 3 |  |  |  |
Energy Relief Fund - Merrimack Valley Programs |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Restricted cash, current |  | $ 20,000,000 | 20,000,000 |  |  |
Restricted cash, noncurrent |  | 16,700,000 | 15,900,000 |  |  |
COVID-19 |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for uncollectible accounts for late fees and other receivable amounts |  | 50,900,000 | 50,900,000 |  |  |
CL&P |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for uncollectible accounts for late fees and other receivable amounts |  | $ 253,400,000 | 225,300,000 |  | 180,500,000 | 181,300,000
Period of accounts receivable recoverable under financial or medical duress |  | 180 days |  |  |  |
CL&P | COVID-19 |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for uncollectible accounts for late fees and other receivable amounts |  | $ 16,000,000 | 16,000,000 |  |  |
NSTAR Electric |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for uncollectible accounts for late fees and other receivable amounts |  | 94,600,000 | 95,000,000.0 |  | 94,800,000 | 97,000,000.0
NSTAR Electric | COVID-19 |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for uncollectible accounts for late fees and other receivable amounts |  | 4,100,000 | 4,100,000 |  |  |
PSNH |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for uncollectible accounts for late fees and other receivable amounts |  | 33,500,000 | 29,200,000 |  | $ 26,200,000 | $ 24,300,000
PSNH | COVID-19 |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for uncollectible accounts for late fees and other receivable amounts |  | $ 0 | $ 0 |  |  |
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 |  |  |  |
Offshore Wind Business |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Ownership interest (percent) |  |  |  | 50.00% |  |
North East Offshore LLC |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Ownership interest (percent) |  | 50.00% |  |  |  |
Renewable Energy Investment Fund |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Ownership interest (percent) |  | 90.00% |  |  |  |
Proceeds from sale of equity method investments | $ 123,400,000 |  |  |  |  |
Renewable Energy Investment Fund | Equity Method Investee |  |  |  |  |  |
Summary of Accounting Policies [Line Items] |  |  |  |  |  |
Charitable contributions |  | $ 20,000,000 |  |  |  |

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