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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, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Components of Other Operating Costs and Expense [Line Items] |  |  |
Borrowed Funds | $ 18.4 | $ 23.7 | $ 25.6
Equity Funds | 37.3 | 42.0 | 45.0
Total AFUDC | $ 55.7 | $ 65.7 | $ 70.6
Average AFUDC Rate | 4.20% | 5.00% | 5.40%
The Connecticut Light and Power Company |  |  |
Components of Other Operating Costs and Expense [Line Items] |  |  |
Borrowed Funds | $ 2.9 | $ 6.6 | $ 7.1
Equity Funds | 7.7 | 13.8 | 13.2
Total AFUDC | $ 10.6 | $ 20.4 | $ 20.3
Average AFUDC Rate | 5.00% | 5.90% | 6.30%
NSTAR Electric Company |  |  |
Components of Other Operating Costs and Expense [Line Items] |  |  |
Borrowed Funds | $ 9.0 | $ 9.1 | $ 10.4
Equity Funds | 20.4 | 21.5 | 19.8
Total AFUDC | $ 29.4 | $ 30.6 | $ 30.2
Average AFUDC Rate | 4.90% | 5.70% | 5.70%
Public Service Company of New Hampshire |  |  |
Components of Other Operating Costs and Expense [Line Items] |  |  |
Borrowed Funds | $ 0.8 | $ 2.1 | $ 2.8
Equity Funds | 1.6 | 4.2 | 3.4
Total AFUDC | $ 2.4 | $ 6.3 | $ 6.2
Average AFUDC Rate | 2.50% | 4.70% | 4.60%

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 + 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 -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 + Details
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- Definition Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 + Details
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