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COMMITMENTS AND CONTINGENCIES - Eversource and NSTAR Electric Boston Harbor Civil Action (Details) $ in Millions | Jul. 15, 2016 kV | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
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Site Contingency [Line Items] |  |  |  |
Amount of capacity required for installation of distribution cable (in kV) | kV | 115 |  |  |
Asset retirement obligations |  | $ 500.1 | $ 499.7 | $ 489.5
NSTAR Electric Company |  |  |  |
Site Contingency [Line Items] |  |  |  |
Asset retirement obligations |  | $ 97.5 | $ 91.8 | $ 97.5

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- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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