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ASSET RETIREMENT OBLIGATIONS | 12 Months Ended
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Dec. 31, 2024
Asset Retirement Obligation Disclosure [Abstract] |
ASSET RETIREMENT OBLIGATIONS | ASSET RETIREMENT OBLIGATIONS Eversource, including CL&P, NSTAR Electric and PSNH, recognizes a liability for the fair value of an ARO on the obligation date if the liability's fair value can be reasonably estimated, even if it is conditional on a future event. Settlement dates and future costs are reasonably estimated when sufficient information becomes available. Management has identified various categories of AROs, primarily CYAPC's and YAEC's obligation to dispose of spent nuclear fuel and high level waste, and also certain assets containing asbestos and hazardous contamination. Management has performed fair value calculations reflecting expected probabilities for settlement scenarios. The fair value of an ARO is recorded as a long-term liability with a corresponding amount included in Property, Plant and Equipment, Net on the balance sheets. The ARO assets are depreciated, and the ARO liabilities are accreted over the estimated life of the obligation and the corresponding credits are recorded as accumulated depreciation and ARO liabilities, respectively. As the electric and natural gas companies are rate-regulated on a cost-of-service basis, these companies apply regulatory accounting guidance and both the depreciation and accretion costs associated with these companies' AROs are recorded as increases to Regulatory Assets on the balance sheets. A reconciliation of the beginning and ending carrying amounts of ARO liabilities is as follows:
| As of December 31,
| 2024 |  | 2023
(Millions of Dollars) | Eversource |  | CL&P |  | NSTAR Electric |  | PSNH |  | Eversource |  | CL&P |  | NSTAR Electric |  | PSNH
Balance as of Beginning of Year | $ | 505.8 |  |  | $ | 39.9 |  |  | $ | 104.8 |  |  | $ | 5.2 |  |  | $ | 502.7 |  |  | $ | 37.4 |  |  | $ | 101.3 |  |  | $ | 4.9 |
Liabilities Settled During the Year | (24.6) |  |  | — |  |  | — |  |  | — |  |  | (24.9) |  |  | — |  |  | — |  |  | — |
Accretion | 29.5 |  |  | 2.6 |  |  | 4.5 |  |  | 0.4 |  |  | 29.2 |  |  | 2.5 |  |  | 4.3 |  |  | 0.3 |
Revisions in Estimated Cash Flows | 80.2 |  |  | — |  |  | — |  |  | — |  |  | (1.2) |  |  | — |  |  | (0.8) |  |  | — |
Balance as of End of Year | $ | 590.9 |  |  | $ | 42.5 |  |  | $ | 109.3 |  |  | $ | 5.6 |  |  | $ | 505.8 |  |  | $ | 39.9 |  |  | $ | 104.8 |  |  | $ | 5.2 |
Eversource's amounts include CYAPC and YAEC's AROs of $391.7 million and $315.8 million as of December 31, 2024 and 2023, respectively. The fair value of the ARO for CYAPC and YAEC includes uncertainties of the fuel off-load dates related to the DOE's timing of performance regarding its obligation to dispose of the spent nuclear fuel and high level waste and other assumptions, including discount rates. The incremental asset recorded as an offset to the ARO liability was fully depreciated since the plants have no remaining useful life. Any changes in the ARO liability are recorded with a corresponding offset to the related regulatory asset. The assets held in the CYAPC and YAEC spent nuclear fuel trusts are restricted for settling the ARO and all other nuclear fuel storage obligations. For further information on the assets held in the spent nuclear fuel trusts, see Note 5, "Marketable Securities," to the financial statements. The increase in the ARO balance at Eversource for the year ended December 31, 2024 was due primarily to updated cost estimates that extended the end of life date from 2039 to 2044 for CYAPC and YAEC. These updated cost estimates were approved by FERC in November 2024.

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- Definition The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481850/410-20-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/410-20/tableOfContent Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -SubTopic 20 -Topic 410 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481850/410-20-50-2 + Details
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