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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Materials, Supplies, Natural Gas, and REC Inventory (Details) - USD ($) $ in Millions | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Public Utilities, Inventory [Line Items] |  |
Total | $ 374.4 | $ 267.5
Materials and Supplies |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 221.0 | 148.9
Natural Gas |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 95.9 | 56.2
RECs |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 57.5 | 62.4
CL&P |  |
Public Utilities, Inventory [Line Items] |  |
Total | 88.2 | 60.3
CL&P | Materials and Supplies |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 88.2 | 60.3
CL&P | Natural Gas |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 0.0 | 0.0
CL&P | RECs |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 0.0 | 0.0
NSTAR Electric |  |
Public Utilities, Inventory [Line Items] |  |
Total | 138.4 | 116.7
NSTAR Electric | Materials and Supplies |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 81.0 | 55.0
NSTAR Electric | Natural Gas |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 0.0 | 0.0
NSTAR Electric | RECs |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 57.4 | 61.7
PSNH |  |
Public Utilities, Inventory [Line Items] |  |
Total | 34.5 | 25.9
PSNH | Materials and Supplies |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 34.4 | 25.2
PSNH | Natural Gas |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | 0.0 | 0.0
PSNH | RECs |  |
Public Utilities, Inventory [Line Items] |  |
Other inventory, capitalized costs, gross | $ 0.1 | $ 0.7

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- Definition Gross amount, as of the balance sheet date, of merchandise, goods, commodities, or supplies held for future sale or to be used in manufacturing, servicing or production process. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(6)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Amount, before valuation and last-in first out (LIFO) reserves, of costs capitalized in inventory classified as other, expected to be sold, or consumed within one year or operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(6)(a)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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