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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AFUDC and Weighted Average AFUDC (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Components of Other Operating Costs and Expense [Line Items] |  |  |
Borrowed Funds | $ 44.6 | $ 21.8 | $ 18.4
Equity Funds | 78.1 | 47.3 | 37.3
Total AFUDC | $ 122.7 | $ 69.1 | $ 55.7
Average AFUDC Rate (in percent) | 5.80% | 4.70% | 4.20%
CL&P |  |  |
Components of Other Operating Costs and Expense [Line Items] |  |  |
Borrowed Funds | $ 7.7 | $ 4.8 | $ 2.9
Equity Funds | 20.0 | 13.6 | 7.7
Total AFUDC | $ 27.7 | $ 18.4 | $ 10.6
Average AFUDC Rate (in percent) | 6.70% | 6.60% | 5.00%
NSTAR Electric |  |  |
Components of Other Operating Costs and Expense [Line Items] |  |  |
Borrowed Funds | $ 17.2 | $ 10.7 | $ 9.0
Equity Funds | 45.7 | 24.6 | 20.4
Total AFUDC | $ 62.9 | $ 35.3 | $ 29.4
Average AFUDC Rate (in percent) | 5.90% | 5.40% | 4.90%
PSNH |  |  |
Components of Other Operating Costs and Expense [Line Items] |  |  |
Borrowed Funds | $ 6.1 | $ 1.4 | $ 0.8
Equity Funds | 5.4 | 2.5 | 1.6
Total AFUDC | $ 11.5 | $ 3.9 | $ 2.4
Average AFUDC Rate (in percent) | 5.10% | 2.60% | 2.50%

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- Definition The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481668/980-835-25-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482064/980-835-45-1 + Details
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- Definition Amount capitalized of allowance for funds used during construction. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481668/980-835-25-1 + Details
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