SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements of Eversource, NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying consolidated financial statements of Eversource, NSTAR Electric and PSNH and the financial statements of CL&P are herein collectively referred to as the "financial statements." The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Eversource consolidates the operations of CYAPC and YAEC, both of which are inactive regional nuclear power companies engaged in the long-term storage of their spent nuclear fuel. Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's and PSNH's combined ownership and voting interests in each of these entities is greater than 50 percent. Intercompany transactions between CL&P, NSTAR Electric, PSNH and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements. Eversource holds several equity ownership interests that are not consolidated and are accounted for under the equity method. In accordance with accounting guidance on noncontrolling interests in consolidated financial statements, the Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric, which are not owned by Eversource or its consolidated subsidiaries and are not subject to mandatory redemption, have been presented as noncontrolling interests in the financial statements of Eversource. The Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric are considered to be temporary equity and have been classified between liabilities and permanent shareholders' equity on the balance sheets of Eversource, CL&P and NSTAR Electric due to a provision in the preferred stock agreements of both CL&P and NSTAR Electric that grant preferred stockholders the right to elect a majority of the CL&P and NSTAR Electric Boards of Directors, respectively, should certain conditions exist, such as if preferred dividends are in arrears for a specified amount of time. The Net Income reported in the statements of income and cash flows represents net income prior to apportionment to noncontrolling interests, which is represented by dividends on preferred stock of CL&P and NSTAR Electric. Eversource's utility subsidiaries' electric, natural gas and water distribution and transmission businesses are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for entities with rate-regulated operations, which considers the effect of regulation on the differences in the timing of the recognition of certain revenues and expenses from those of other businesses and industries. See Note 2, "Regulatory Accounting," for further information. COVID-19 has adversely affected workers and the economy and caused volatility in the financial markets. Due to the inherent uncertainty of the unprecedented and evolving situation, we continue to closely monitor how COVID-19 related developments affect Eversource. Based on available information, we have not experienced significant impacts directly related to the pandemic that have adversely affected our current operations or results of operations. The extent of the impact to us in the future will vary and depend in large part on the duration, scope and severity of the pandemic and the timing and extent of COVID-19 relief legislation, and the resulting impact on economic, health care and capital market conditions. The future impact will also depend on the outcome of planned proceedings before our state regulatory commissions to recover our incremental costs associated with COVID-19. We believe that we have in place, or are developing, successful mechanisms with our state regulatory commissions that allow, or will allow, us to recover our incremental costs associated with COVID-19, which include uncollectible customer receivable expenses, while balancing the impact on our customers’ bills and our operating cash flows. See Note 1F, "Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts," for discussion of our evaluation of the allowance for doubtful accounts as of December 31, 2020 in light of the COVID-19 pandemic. An extended economic slowdown has resulted in lower demand for electricity, natural gas and/or water by our commercial and industrial customers. However, fluctuations in retail sales volumes for CL&P, NSTAR Electric, Yankee Gas, NSTAR Gas, EGMA, and our Connecticut water distribution business do not materially impact earnings due to their respective state regulatory commission-approved distribution revenue decoupling mechanisms. As of December 31, 2020, we did not identify indicators or triggering events for impairments to our goodwill, long-lived assets, available-for-sale debt securities, or equity method investment carrying values. Certain reclassifications of prior year data were made in the accompanying financial statements to conform to the current year presentation.
Accounting Standards	Accounting Standards Accounting Standards Issued but Not Yet Effective: In December 2019, the FASB issued Accounting Standards Update (ASU) 2019-12, Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes, which eliminates certain exceptions to the general principles of current income tax guidance in ASC 740 and simplifies and improves consistency in application of that income tax guidance through clarifications of and amendments to ASC 740. The guidance is effective in the first quarter of 2021. The ASU is not expected to have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric and PSNH. Accounting Standards Recently Adopted: On January 1, 2020, the Company adopted ASU 2016-13, Financial Instruments - Credit Losses (Topic 326), which provides a model for recognizing credit losses on financial instruments based on an estimate of current expected losses, requiring immediate recognition of credit losses expected over the life of a financial instrument. The Company determined the impacts of this standard on the allowance for credit losses on its financial instruments, primarily accounts receivable. As of January 1, 2020, the Company recorded increases to the allowance for uncollectible accounts for late fees and other receivable amounts of $1.6 million, $0.9 million, $0.2 million and $0.3 million at Eversource, CL&P, NSTAR Electric and PSNH, respectively. The impact to retained earnings, net of tax, was $1.5 million, $0.9 million, $0.2 million and $0.3 million at Eversource, CL&P, NSTAR Electric and PSNH, respectively. The Company also adjusted the allowance for uncollectible amounts of hardship receivables and other low-income assistance programs, which are ultimately collectible in rates at specified points in time under approved regulatory mechanisms. The impact on the allowance, which was offset in other long-term assets on the balance sheets, was an increase of $22.2 million and $21.3 million at Eversource and CL&P, respectively, and a decrease of $1.5 million at NSTAR Electric as of January 1, 2020. See Note 1F, “Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts,” for further information. The Company adopted ASU 2017-04, Intangibles - Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment as of January 1, 2020. The ASU simplified the accounting for goodwill impairment by removing a complex step in the goodwill impairment test. Under the guidance, goodwill impairment is measured as the amount by which its carrying value exceeds its fair value. The ASU did not have an impact on the financial statements of Eversource. On January 1, 2020, the Company adopted ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40) - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The ASU aligned the requirements for capitalizing costs incurred to implement a cloud computing arrangement with existing internal-use software guidance. The prospective implementation of this standard did not have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric or PSNH for the year ended December 31, 2020. On January 1, 2020, the Company prospectively adopted ASU 2018-13, Fair Value Measurement (Topic 820), Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. The ASU modified fair value disclosure requirements. The standard includes new disclosure requirements for Level 3 unobservable inputs and eliminated the requirement to disclose certain information relating to transfers between levels. The modified disclosures are included in Note 1I, “Summary of Significant Accounting Policies - Fair Value Measurements,” and Note 4, “Derivative Instruments.” The Company adopted ASU 2018-14, Compensation – Retirement Benefits – Defined Benefit Plans – General, Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans as of January 1, 2020. The guidance eliminated certain disclosures about defined benefit plans, added new disclosures, and clarified other requirements. This guidance is effective for fiscal years ending after December 15, 2020. Adoption of this guidance did not have a material effect on our annual financial statement disclosures. The modified disclosures are included in Note 11A, “Employee Benefits - Pension Benefits and Postretirement Benefits Other Than Pension.”
Cash	CashCash includes cash on hand. At the end of each reporting period, any overdraft amounts are reclassified from Cash to Accounts Payable on the balance sheets.
Provision for Uncollectible Accounts	Allowance for Uncollectible Accounts Receivables, Net on the balance sheets primarily includes trade receivables from retail customers and customers related to wholesale transmission contracts, wholesale market sales, sales of RECs and property rentals. Receivables, Net also includes customer receivables for the purchase of electricity from a competitive third party supplier, the current portion of customer energy efficiency loans, property damage receivables and other miscellaneous receivables. There is no material concentration of receivables. Receivables are recorded at amortized cost, net of a credit loss provision (or allowance for uncollectible accounts). Receivables are presented net of expected credit losses at estimated net realizable value by maintaining an allowance for uncollectible accounts. Effective January 1, 2020, the current expected credit loss (CECL) model was applied to receivables for purposes of calculating the allowance for uncollectible accounts. This model is based on expected losses and results in the recognition of estimated expected credit losses, including uncollectible amounts for both billed and unbilled revenues, over the life of the receivable at the time a receivable is recorded. Receivables, net of reserves, increased $206.5 million ($58.3 million at CL&P, $56.3 million at NSTAR Electric, and $20.0 million at PSNH) in 2020, as compared to 2019, due primarily to an increase in delinquent receivables from customers attributable to the moratorium on disconnections and the economic slowdown resulting from the COVID-19 pandemic. Receivables, net of reserves, also increased due to the addition of EGMA of $65.8 million as of December 31, 2020. The allowance for uncollectible accounts is determined based upon a variety of judgments and factors, including the application of an estimated uncollectible percentage to each receivable aging category. Factors in determining credit loss include historical collection, write-off experience, and management's assessment of collectability from customers, including current conditions, reasonable forecasts, and expectations of future collectability and collection efforts. Management continuously assesses the collectability of receivables and adjusts estimates based on actual experience and future expectations based on economic indicators, collection efforts and other factors. Management also monitors the aging analysis of receivables to determine if there are changes in the collections of accounts receivable. Receivable balances are written off against the allowance for uncollectible accounts when the customer accounts are no longer in service and these balances are deemed to be uncollectible. As of December 31, 2020, management evaluated the adequacy of the allowance for uncollectible accounts in light of the COVID-19 pandemic and the related economic downturn. This evaluation included an analysis of collection and customer payment trends, economic conditions, delinquency statistics, aging-based quantitative assessments, the impact on residential customer bills because of energy usage and change in rates, flexible payment plans and financial hardship arrearage management programs being offered to customers, and COVID-19 developments, including any potential federal governmental pandemic relief programs and the expansion of unemployment benefit initiatives, which help to mitigate the potential for increasing customer account delinquencies. Additionally, management considered past economic declines and corresponding uncollectible reserves as part of the current assessment. This evaluation has shown that our operating companies have experienced an increase in aged receivables and some lower cash collections from customers because of the moratorium on disconnections and the economic slowdown resulting from the COVID-19 pandemic. Based upon the evaluation performed, for the year ended December 31, 2020, management increased the allowance for uncollectible accounts for amounts incurred as a result of COVID-19 by $31.5 million for Eversource ($2.8 million for CL&P, $11.0 million for NSTAR Electric, $2.3 million for PSNH and $15.4 million at our natural gas businesses). These COVID-19 related uncollectible amounts were deferred either as incremental regulatory costs or deferred through existing regulatory tracking mechanisms that recover uncollectible energy supply costs, as management believes it is probable that these costs will ultimately be recovered from customers in rates. Management concluded that the reserve balance as of December 31, 2020 adequately reflected the collection risk and net realizable value for Eversource’s receivables. Management will continue to evaluate the adequacy of the uncollectible allowance in future reporting periods based on an ongoing assessment of accounts receivable collections, delinquency statistics, and analysis of aging-based quantitative assessments. The PURA allows CL&P and Yankee Gas to accelerate the recovery of accounts receivable balances attributable to qualified customers under financial or medical duress (uncollectible hardship accounts receivable) outstanding for greater than 180 days and 90 days, respectively. The DPU allows NSTAR Electric and NSTAR Gas to recover in rates, amounts associated with certain uncollectible hardship accounts receivable. Management also believes that uncollectible hardship accounts receivable at EGMA will be recoverable in future rates. These uncollectible hardship customer account balances are included in Regulatory Assets or Other Long-Term Assets on the balance sheets. Hardship customers are protected from shut-off in certain circumstances, and historical collection experience has reflected a higher default risk as compared to the rest of the receivable population. As a result of the adoption of ASU 2016-13, management aligned the allowance for uncollectible hardship accounts across all regulatory jurisdictions, using a higher credit risk profile for this pool of trade receivables as compared to non-hardship receivables. Implementation impacts of the accounting standard on the allowance for uncollectible hardship accounts are reflected in the rollforward of the uncollectible allowance in the table below. The allowance for uncollectible hardship accounts is included in the total uncollectible allowance balance.
Transfer of Energy Efficiency Loans	Transfer of Energy Efficiency LoansCL&P has transferred a portion of its energy efficiency customer loan portfolio to outside lenders in order to make additional loans to customers. CL&P remains the servicer of the loans and will transmit customer payments to the lenders, with a maximum amount outstanding under this program of $55 million. The amounts of the loans are included in Accounts Receivable, Net and Other Long-Term Assets, and are offset by Other Current Liabilities and Other Long-Term Liabilities on CL&P’s balance sheet.
Fuel, Materials, Supplies and REC Inventory	Fuel, Materials, Supplies and REC InventoryFuel, Materials, Supplies and REC Inventory include natural gas inventory, materials and supplies purchased primarily for construction or operation and maintenance purposes, and RECs. Inventory is valued at the lower of cost or net realizable value. RECs are purchased from suppliers of renewable sources of generation and are used to meet state mandated Renewable Portfolio Standards requirements.
Fair Value Measurements	Fair Value Measurements Fair value measurement guidance is applied to derivative contracts that are not elected or designated as "normal purchases" or "normal sales" (normal) and to the marketable securities held in trusts. Fair value measurement guidance is also applied to valuations of the investments used to calculate the funded status of pension and PBOP plans, the nonrecurring fair value measurements of nonfinancial assets such as goodwill, long-lived assets, equity method investments, and AROs, and in the valuation of the acquisition of CMA in 2020. The fair value measurement guidance was also applied in estimating the fair value of preferred stock, long-term debt and RRBs. Fair Value Hierarchy: In measuring fair value, Eversource uses observable market data when available in order to minimize the use of unobservable inputs. Inputs used in fair value measurements are categorized into three fair value hierarchy levels for disclosure purposes. The entire fair value measurement is categorized based on the lowest level of input that is significant to the fair value measurement. Eversource evaluates the classification of assets and liabilities measured at fair value on a quarterly basis. The levels of the fair value hierarchy are described below: Level 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable. Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products. Uncategorized - Investments that are measured at net asset value are not categorized within the fair value hierarchy.
Derivative Accounting	Derivative Accounting Many of the electric and natural gas companies' contracts for the purchase and sale of energy or energy-related products are derivatives. The accounting treatment for energy contracts entered into varies and depends on the intended use of the particular contract and on whether or not the contract is a derivative. The application of derivative accounting is complex and requires management judgment in the following respects: identification of derivatives and embedded derivatives, election and designation of a contract as normal, and determination of the fair value of derivative contracts. All of these judgments can have a significant impact on the financial statements. The judgment applied in the election of a contract as normal (and resulting accrual accounting) includes the conclusion that it is probable at the inception of the contract and throughout its term that it will result in physical delivery of the underlying product and that the quantities will be used or sold by the business in the normal course of business. If facts and circumstances change and management can no longer support this conclusion, then a contract cannot be considered normal, accrual accounting is terminated, and fair value accounting is applied prospectively. The fair value of derivative contracts is based upon the contract terms and conditions and the underlying market price or fair value per unit. When quantities are not specified in the contract, the Company determines whether the contract has a determinable quantity by using amounts referenced in default provisions and other relevant sections of the contract. The fair value of derivative assets and liabilities with the same counterparty are offset and recorded as a net derivative asset or liability on the balance sheets. Regulatory assets or regulatory liabilities are recorded to offset the fair values of derivative contracts related to energy and energy-related products, as contract settlements are recovered from, or refunded to, customers in future rates. All changes in the fair value of derivative contracts are recorded as regulatory assets or liabilities and do not impact net income.
Allowance for Funds Used During Construction	Allowance for Funds Used During ConstructionAFUDC represents the cost of borrowed and equity funds used to finance construction and is included in the cost of the electric, natural gas and water companies' utility plant on the balance sheet. The portion of AFUDC attributable to borrowed funds is recorded as a reduction of Interest Expense, and the AFUDC related to equity funds is recorded as Other Income, Net on the statements of income. AFUDC costs are recovered from customers over the service life of the related plant in the form of increased revenue collected as a result of higher depreciation expense. The average AFUDC rate is based on a FERC-prescribed formula using the cost of a company's short-term financings and capitalization (preferred stock, long-term debt and common equity), as appropriate. The average rate is applied to average eligible CWIP amounts to calculate AFUDC.
Other Taxes	Other TaxesEversource's companies that serve customers in Connecticut collect gross receipts taxes levied by the state of Connecticut from their customers. Separate from above were amounts recorded as Taxes Other Than Income Taxes at CL&P related to the remittance to the State of Connecticut of energy efficiency funds collected from customers of $21.4 million and $46.8 million in 2019 and 2018, respectively. Energy efficiency funds collected from customers after July 1, 2019 are no longer subject to remittance to the State of Connecticut. These amounts were recorded separately, with collections in Operating Revenues and with payments in Taxes Other Than Income Taxes on the Eversource and CL&P statements of income. As agents for state and local governments, Eversource's companies that serve customers in Connecticut and Massachusetts collect certain sales taxes that are recorded on a net basis with no impact on the statements of income.
Related Parties	Related Parties Eversource Service, Eversource's service company, provides centralized accounting, administrative, engineering, financial, information technology, legal, operational, planning, purchasing, tax, and other services to Eversource's companies. The Rocky River Realty Company and Properties, Inc., two other Eversource subsidiaries, construct, acquire or lease some of the property and facilities used by Eversource's companies. As of both December 31, 2020 and 2019, CL&P, NSTAR Electric and PSNH had long-term receivables from Eversource Service in the amounts of $25.0 million, $5.5 million and $3.8 million, respectively, which were included in Other Long-Term Assets on the balance sheets. These amounts related to the funding of investments held in trust by Eversource Service in connection with certain postretirement benefits for CL&P, NSTAR Electric and PSNH employees and have been eliminated in consolidation on the Eversource financial statements. Included in the CL&P, NSTAR Electric and PSNH balance sheets as of December 31, 2020 and 2019 were Accounts Receivable from Affiliated Companies and Accounts Payable to Affiliated Companies relating to transactions between CL&P, NSTAR Electric and PSNH and other subsidiaries that are wholly-owned by Eversource. These amounts have been eliminated in consolidation on the Eversource financial statements. The Eversource Energy Foundation is an independent not-for-profit charitable entity and is not included in the consolidated financial statements of Eversource as the Company does not have title to, and cannot receive contributions back from, the Eversource Energy Foundation's assets. Eversource made contributions to the Eversource Energy Foundation of $6.4 million in 2020 and did not make any contributions in 2019 or 2018.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

12 Months Ended

Dec. 31, 2020

The consolidated financial statements of Eversource, NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying consolidated financial statements of Eversource, NSTAR Electric and PSNH and the financial statements of CL&P are herein collectively referred to as the "financial statements."

The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

Eversource consolidates the operations of CYAPC and YAEC, both of which are inactive regional nuclear power companies engaged in the long-term storage of their spent nuclear fuel. Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's and PSNH's combined ownership and voting interests in each of these entities is greater than 50 percent. Intercompany transactions between CL&P, NSTAR Electric, PSNH and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements.

Eversource holds several equity ownership interests that are not consolidated and are accounted for under the equity method.

In accordance with accounting guidance on noncontrolling interests in consolidated financial statements, the Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric, which are not owned by Eversource or its consolidated subsidiaries and are not subject to mandatory redemption, have been presented as noncontrolling interests in the financial statements of Eversource. The Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric are considered to be temporary equity and have been classified between liabilities and permanent shareholders' equity on the balance sheets of Eversource, CL&P and NSTAR Electric due to a provision in the preferred stock agreements of both CL&P and NSTAR Electric that grant preferred stockholders the right to elect a majority of the CL&P and NSTAR Electric Boards of Directors, respectively, should certain conditions exist, such as if preferred dividends are in arrears for a specified amount of time. The Net Income reported in the statements of income and cash flows represents net income prior to apportionment to noncontrolling interests, which is represented by dividends on preferred stock of CL&P and NSTAR Electric.

Eversource's utility subsidiaries' electric, natural gas and water distribution and transmission businesses are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for entities with rate-regulated operations, which considers the effect of regulation on the differences in the timing of the recognition of certain revenues and expenses from those of other businesses and industries. See Note 2, "Regulatory Accounting," for further information.

COVID-19 has adversely affected workers and the economy and caused volatility in the financial markets. Due to the inherent uncertainty of the unprecedented and evolving situation, we continue to closely monitor how COVID-19 related developments affect Eversource. Based on available information, we have not experienced significant impacts directly related to the pandemic that have adversely affected our current operations or results of operations. The extent of the impact to us in the future will vary and depend in large part on the duration, scope and severity of the pandemic and the timing and extent of COVID-19 relief legislation, and the resulting impact on economic, health care and capital market conditions. The future impact will also depend on the outcome of planned proceedings before our state regulatory commissions to recover our incremental costs associated with COVID-19.

We believe that we have in place, or are developing, successful mechanisms with our state regulatory commissions that allow, or will allow, us to recover our incremental costs associated with COVID-19, which include uncollectible customer receivable expenses, while balancing the impact on our customers’ bills and our operating cash flows. See Note 1F, "Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts," for discussion of our evaluation of the allowance for doubtful accounts as of December 31, 2020 in light of the COVID-19 pandemic.

An extended economic slowdown has resulted in lower demand for electricity, natural gas and/or water by our commercial and industrial customers. However, fluctuations in retail sales volumes for CL&P, NSTAR Electric, Yankee Gas, NSTAR Gas, EGMA, and our Connecticut water distribution business do not materially impact earnings due to their respective state regulatory commission-approved distribution revenue decoupling mechanisms.

As of December 31, 2020, we did not identify indicators or triggering events for impairments to our goodwill, long-lived assets, available-for-sale debt securities, or equity method investment carrying values.

Certain reclassifications of prior year data were made in the accompanying financial statements to conform to the current year presentation.

Accounting Standards

Accounting Standards Issued but Not Yet Effective: In December 2019, the FASB issued Accounting Standards Update (ASU) 2019-12, Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes, which eliminates certain exceptions to the general principles of current income tax guidance in ASC 740 and simplifies and improves consistency in application of that income tax guidance through clarifications of and amendments to ASC 740. The guidance is effective in the first quarter of 2021. The ASU is not expected to have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric and PSNH.

Accounting Standards Recently Adopted: On January 1, 2020, the Company adopted ASU 2016-13, Financial Instruments - Credit Losses (Topic 326), which provides a model for recognizing credit losses on financial instruments based on an estimate of current expected losses, requiring immediate recognition of credit losses expected over the life of a financial instrument. The Company determined the impacts of this standard on the allowance for credit losses on its financial instruments, primarily accounts receivable. As of January 1, 2020, the Company recorded increases to the allowance for uncollectible accounts for late fees and other receivable amounts of $1.6 million, $0.9 million, $0.2 million and $0.3 million at Eversource, CL&P, NSTAR Electric and PSNH, respectively. The impact to retained earnings, net of tax, was $1.5 million, $0.9 million, $0.2 million and $0.3 million at Eversource, CL&P, NSTAR Electric and PSNH, respectively.

The Company also adjusted the allowance for uncollectible amounts of hardship receivables and other low-income assistance programs, which are ultimately collectible in rates at specified points in time under approved regulatory mechanisms. The impact on the allowance, which was offset in other long-term assets on the balance sheets, was an increase of $22.2 million and $21.3 million at Eversource and CL&P, respectively, and a decrease of $1.5 million at NSTAR Electric as of January 1, 2020. See Note 1F, “Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts,” for further information.

The Company adopted ASU 2017-04, Intangibles - Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment as of January 1, 2020. The ASU simplified the accounting for goodwill impairment by removing a complex step in the goodwill impairment test. Under the guidance, goodwill impairment is measured as the amount by which its carrying value exceeds its fair value. The ASU did not have an impact on the financial statements of Eversource.

On January 1, 2020, the Company adopted ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40) - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The ASU aligned the requirements for capitalizing costs incurred to implement a cloud computing arrangement with existing internal-use software guidance. The prospective implementation of this standard did not have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric or PSNH for the year ended December 31, 2020.

On January 1, 2020, the Company prospectively adopted ASU 2018-13, Fair Value Measurement (Topic 820), Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. The ASU modified fair value disclosure requirements. The standard includes new disclosure requirements for Level 3 unobservable inputs and eliminated the requirement to disclose certain information relating to transfers between levels. The modified disclosures are included in Note 1I, “Summary of Significant Accounting Policies - Fair Value Measurements,” and Note 4, “Derivative Instruments.”

The Company adopted ASU 2018-14, Compensation – Retirement Benefits – Defined Benefit Plans – General, Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans as of January 1, 2020. The guidance eliminated certain disclosures about defined benefit plans, added new disclosures, and clarified other requirements. This guidance is effective for fiscal years ending after December 15, 2020. Adoption of this guidance did not have a material effect on our annual financial statement disclosures. The modified disclosures are included in Note 11A, “Employee Benefits - Pension Benefits and Postretirement Benefits Other Than Pension.”

Cash

CashCash includes cash on hand. At the end of each reporting period, any overdraft amounts are reclassified from Cash to Accounts Payable on the balance sheets.

Provision for Uncollectible Accounts

Allowance for Uncollectible Accounts

Receivables, Net on the balance sheets primarily includes trade receivables from retail customers and customers related to wholesale transmission contracts, wholesale market sales, sales of RECs and property rentals. Receivables, Net also includes customer receivables for the purchase of electricity from a competitive third party supplier, the current portion of customer energy efficiency loans, property damage receivables and other miscellaneous receivables. There is no material concentration of receivables. Receivables are recorded at amortized cost, net of a credit loss provision (or allowance for uncollectible accounts).

Receivables are presented net of expected credit losses at estimated net realizable value by maintaining an allowance for uncollectible accounts. Effective January 1, 2020, the current expected credit loss (CECL) model was applied to receivables for purposes of calculating the allowance for uncollectible accounts. This model is based on expected losses and results in the recognition of estimated expected credit losses, including uncollectible amounts for both billed and unbilled revenues, over the life of the receivable at the time a receivable is recorded.

Receivables, net of reserves, increased $206.5 million ($58.3 million at CL&P, $56.3 million at NSTAR Electric, and $20.0 million at PSNH) in 2020, as compared to 2019, due primarily to an increase in delinquent receivables from customers attributable to the moratorium on disconnections and the economic slowdown resulting from the COVID-19 pandemic. Receivables, net of reserves, also increased due to the addition of EGMA of $65.8 million as of December 31, 2020.

The allowance for uncollectible accounts is determined based upon a variety of judgments and factors, including the application of an estimated uncollectible percentage to each receivable aging category. Factors in determining credit loss include historical collection, write-off experience, and management's assessment of collectability from customers, including current conditions, reasonable forecasts, and expectations of future collectability and collection efforts. Management continuously assesses the collectability of receivables and adjusts estimates based on actual experience and future expectations based on economic indicators, collection efforts and other factors. Management also monitors the aging analysis of receivables to determine if there are changes in the collections of accounts receivable. Receivable balances are written off against the allowance for uncollectible accounts when the customer accounts are no longer in service and these balances are deemed to be uncollectible.

As of December 31, 2020, management evaluated the adequacy of the allowance for uncollectible accounts in light of the COVID-19 pandemic and the related economic downturn. This evaluation included an analysis of collection and customer payment trends, economic conditions, delinquency statistics, aging-based quantitative assessments, the impact on residential customer bills because of energy usage and change in rates, flexible payment plans and financial hardship arrearage management programs being offered to customers, and COVID-19 developments, including any potential federal governmental pandemic relief programs and the expansion of unemployment benefit initiatives, which help to mitigate the potential for increasing customer account delinquencies. Additionally, management considered past economic declines and corresponding uncollectible reserves as part of the current assessment. This evaluation has shown that our operating companies have experienced an increase in aged receivables and some lower cash collections from customers because of the moratorium on disconnections and the economic slowdown resulting from the COVID-19 pandemic. Based upon the evaluation performed, for the year ended December 31, 2020, management increased the allowance for uncollectible accounts for amounts incurred as a result of COVID-19 by $31.5 million for Eversource ($2.8 million for CL&P, $11.0 million for NSTAR Electric, $2.3 million for PSNH and $15.4 million at our natural gas businesses). These COVID-19 related uncollectible amounts were deferred either as incremental regulatory costs or deferred through existing regulatory tracking mechanisms that recover uncollectible energy supply costs, as management believes it is probable that these costs will ultimately be recovered from customers in rates.

Management concluded that the reserve balance as of December 31, 2020 adequately reflected the collection risk and net realizable value for Eversource’s receivables. Management will continue to evaluate the adequacy of the uncollectible allowance in future reporting periods based on an ongoing assessment of accounts receivable collections, delinquency statistics, and analysis of aging-based quantitative assessments.

The PURA allows CL&P and Yankee Gas to accelerate the recovery of accounts receivable balances attributable to qualified customers under financial or medical duress (uncollectible hardship accounts receivable) outstanding for greater than 180 days and 90 days, respectively. The DPU allows NSTAR Electric and NSTAR Gas to recover in rates, amounts associated with certain uncollectible hardship accounts receivable. Management also believes that uncollectible hardship accounts receivable at EGMA will be recoverable in future rates. These uncollectible hardship customer account balances are included in Regulatory Assets or Other Long-Term Assets on the balance sheets. Hardship customers are protected from shut-off in certain circumstances, and historical collection experience has reflected a higher default risk as compared to the rest of the receivable population. As a result of the adoption of ASU 2016-13, management aligned the allowance for uncollectible hardship accounts across all regulatory jurisdictions, using a higher credit risk profile for this pool of trade receivables as compared to non-hardship receivables. Implementation impacts of the accounting standard on the allowance for uncollectible hardship accounts are reflected in the rollforward of the uncollectible allowance in the table below. The allowance for uncollectible hardship accounts is included in the total uncollectible allowance balance.

Transfer of Energy Efficiency Loans

Transfer of Energy Efficiency LoansCL&P has transferred a portion of its energy efficiency customer loan portfolio to outside lenders in order to make additional loans to customers. CL&P remains the servicer of the loans and will transmit customer payments to the lenders, with a maximum amount outstanding under this program of $55 million. The amounts of the loans are included in Accounts Receivable, Net and Other Long-Term Assets, and are offset by Other Current Liabilities and Other Long-Term Liabilities on CL&P’s balance sheet.

Fuel, Materials, Supplies and REC Inventory

Fuel, Materials, Supplies and REC InventoryFuel, Materials, Supplies and REC Inventory include natural gas inventory, materials and supplies purchased primarily for construction or operation and maintenance purposes, and RECs. Inventory is valued at the lower of cost or net realizable value. RECs are purchased from suppliers of renewable sources of generation and are used to meet state mandated Renewable Portfolio Standards requirements.

Fair Value Measurements

Fair value measurement guidance is applied to derivative contracts that are not elected or designated as "normal purchases" or "normal sales" (normal) and to the marketable securities held in trusts. Fair value measurement guidance is also applied to valuations of the investments used to calculate the funded status of pension and PBOP plans, the nonrecurring fair value measurements of nonfinancial assets such as goodwill, long-lived assets, equity method investments, and AROs, and in the valuation of the acquisition of CMA in 2020. The fair value measurement guidance was also applied in estimating the fair value of preferred stock, long-term debt and RRBs.

Fair Value Hierarchy: In measuring fair value, Eversource uses observable market data when available in order to minimize the use of unobservable inputs. Inputs used in fair value measurements are categorized into three fair value hierarchy levels for disclosure purposes. The entire fair value measurement is categorized based on the lowest level of input that is significant to the fair value measurement. Eversource evaluates the classification of assets and liabilities measured at fair value on a quarterly basis. The levels of the fair value hierarchy are described below:

Level 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis.

Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable.

Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products.

Uncategorized - Investments that are measured at net asset value are not categorized within the fair value hierarchy.

Derivative Accounting

Many of the electric and natural gas companies' contracts for the purchase and sale of energy or energy-related products are derivatives. The accounting treatment for energy contracts entered into varies and depends on the intended use of the particular contract and on whether or not the contract is a derivative.

The application of derivative accounting is complex and requires management judgment in the following respects: identification of derivatives and embedded derivatives, election and designation of a contract as normal, and determination of the fair value of derivative contracts. All of these judgments can have a significant impact on the financial statements. The judgment applied in the election of a contract as normal (and resulting accrual accounting) includes the conclusion that it is probable at the inception of the contract and throughout its term that it will result in physical delivery of the underlying product and that the quantities will be used or sold by the business in the normal course of business. If facts and circumstances change and management can no longer support this conclusion, then a contract cannot be considered normal, accrual accounting is terminated, and fair value accounting is applied prospectively.

The fair value of derivative contracts is based upon the contract terms and conditions and the underlying market price or fair value per unit. When quantities are not specified in the contract, the Company determines whether the contract has a determinable quantity by using amounts referenced in default provisions and other relevant sections of the contract. The fair value of derivative assets and liabilities with the same counterparty are offset and recorded as a net derivative asset or liability on the balance sheets.

Regulatory assets or regulatory liabilities are recorded to offset the fair values of derivative contracts related to energy and energy-related products, as contract settlements are recovered from, or refunded to, customers in future rates. All changes in the fair value of derivative contracts are recorded as regulatory assets or liabilities and do not impact net income.

Allowance for Funds Used During Construction

Allowance for Funds Used During ConstructionAFUDC represents the cost of borrowed and equity funds used to finance construction and is included in the cost of the electric, natural gas and water companies' utility plant on the balance sheet. The portion of AFUDC attributable to borrowed funds is recorded as a reduction of Interest Expense, and the AFUDC related to equity funds is recorded as Other Income, Net on the statements of income. AFUDC costs are recovered from customers over the service life of the related plant in the form of increased revenue collected as a result of higher depreciation expense. The average AFUDC rate is based on a FERC-prescribed formula using the cost of a company's short-term financings and capitalization (preferred stock, long-term debt and common equity), as appropriate. The average rate is applied to average eligible CWIP amounts to calculate AFUDC.

Other Taxes

Other TaxesEversource's companies that serve customers in Connecticut collect gross receipts taxes levied by the state of Connecticut from their customers. Separate from above were amounts recorded as Taxes Other Than Income Taxes at CL&P related to the remittance to the State of Connecticut of energy efficiency funds collected from customers of $21.4 million and $46.8 million in 2019 and 2018, respectively. Energy efficiency funds collected from customers after July 1, 2019 are no longer subject to remittance to the State of Connecticut. These amounts were recorded separately, with collections in Operating Revenues and with payments in Taxes Other Than Income Taxes on the Eversource and CL&P statements of income. As agents for state and local governments, Eversource's companies that serve customers in Connecticut and Massachusetts collect certain sales taxes that are recorded on a net basis with no impact on the statements of income.

Related Parties

Eversource Service, Eversource's service company, provides centralized accounting, administrative, engineering, financial, information technology, legal, operational, planning, purchasing, tax, and other services to Eversource's companies. The Rocky River Realty Company and Properties, Inc., two other Eversource subsidiaries, construct, acquire or lease some of the property and facilities used by Eversource's companies.

As of both December 31, 2020 and 2019, CL&P, NSTAR Electric and PSNH had long-term receivables from Eversource Service in the amounts of $25.0 million, $5.5 million and $3.8 million, respectively, which were included in Other Long-Term Assets on the balance sheets. These amounts related to the funding of investments held in trust by Eversource Service in connection with certain postretirement benefits for CL&P, NSTAR Electric and PSNH employees and have been eliminated in consolidation on the Eversource financial statements.

Included in the CL&P, NSTAR Electric and PSNH balance sheets as of December 31, 2020 and 2019 were Accounts Receivable from Affiliated Companies and Accounts Payable to Affiliated Companies relating to transactions between CL&P, NSTAR Electric and PSNH and other subsidiaries that are wholly-owned by Eversource. These amounts have been eliminated in consolidation on the Eversource financial statements.

The Eversource Energy Foundation is an independent not-for-profit charitable entity and is not included in the consolidated financial statements of Eversource as the Company does not have title to, and cannot receive contributions back from, the Eversource Energy Foundation's assets. Eversource made contributions to the Eversource Energy Foundation of $6.4 million in 2020 and did not make any contributions in 2019 or 2018.