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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Operating Expenses (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Summary of Accounting Policies [Line Items] |  |  |
Natural gas and fuel costs | $ 718.6 | $ 464.2 | $ 462.1

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- Definition Fuel power costs included in Fuel, Purchased and Net Interchange line item on the income statement + References No definition available. + Details
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Namespace Prefix: | es_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition [Line Items] for Summary of Accounting Policies [Table] + References No definition available. + Details
Name: | es_SummaryofAccountingPoliciesLineItems
Namespace Prefix: | es_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration