XML 173 R145.htm IDEA: XBRL DOCUMENT
v3.25.0.1

COMMITMENTS AND CONTINGENCIES - Environmental Matters Narrative (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2024 USD ($) site | Dec. 31, 2023 USD ($) site | Dec. 31, 2022 USD ($)
Loss Contingencies [Line Items] |  |  |
Number of sites | site | 65 | 65 |
Reserve | $ 128.0 | $ 128.2 | $ 122.6
NSTAR Electric |  |  |
Loss Contingencies [Line Items] |  |  |
Number of sites | site | 14 | 12 |
Reserve | $ 6.6 | $ 5.4 | 3.4
CL&P |  |  |
Loss Contingencies [Line Items] |  |  |
Number of sites | site | 15 | 16 |
Reserve | $ 13.4 | $ 13.8 | 13.9
PSNH |  |  |
Loss Contingencies [Line Items] |  |  |
Number of sites | site | 8 | 8 |
Reserve | $ 6.3 | $ 7.6 | $ 6.1
MGP Site accrual |  |  |
Loss Contingencies [Line Items] |  |  |
Reserve balances related to former MGP sites | $ 115.9 | $ 117.1 |
Environmental Site for Which a Range is Too Early to Determine |  |  |
Loss Contingencies [Line Items] |  |  |
Number of sites | site | 17 |  |
Reserve | $ 30.7 |  |
Environmental Site for Which a Range is Too Early to Determine | NSTAR Electric |  |  |
Loss Contingencies [Line Items] |  |  |
Number of sites | site | 2 |  |
Reserve | $ 1.4 |  |
Environmental Site for Which a Range is Too Early to Determine | CL&P |  |  |
Loss Contingencies [Line Items] |  |  |
Number of sites | site | 9 |  |
Reserve | $ 5.7 |  |
Environmental Sites for Which a Range of Loss Exists |  |  |
Loss Contingencies [Line Items] |  |  |
Number of sites | site | 8 |  |
Reserve | $ 29.5 |  |
Best estimate of potential remediation costs (up to) | $ 17.5 |  |
Evironmental Sites with Best Estimate |  |  |
Loss Contingencies [Line Items] |  |  |
Number of sites | site | 40 |  |
Reserve | $ 67.8 |  |
Evironmental Sites with Best Estimate | NSTAR Electric |  |  |
Loss Contingencies [Line Items] |  |  |
Reserve | $ 5.2 |  |
Environmental site quantity remaining | site | 11 |  |
Evironmental Sites with Best Estimate | CL&P |  |  |
Loss Contingencies [Line Items] |  |  |
Reserve | $ 7.7 |  |
Environmental site quantity remaining | site | 6 |  |
Evironmental Sites with Best Estimate | PSNH |  |  |
Loss Contingencies [Line Items] |  |  |
Reserve | $ 6.3 |  |
Environmental site quantity remaining | site | 8 |  |

X
- Definition Number of environmental sites by NU Entity in the remediation or long-term monitoring phase + References No definition available. + Details
Name: | es_EnvironmentalSiteQuantity
Namespace Prefix: | es_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Environmental Site Quantity Remaining + References No definition available. + Details
Name: | es_EnvironmentalSiteQuantityRemaining
Namespace Prefix: | es_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 450 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483076/450-20-50-1 Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Topic 410 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Subparagraph (d)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481931/410-30-50-10 Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Topic 410 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Subparagraph (d)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481931/410-30-50-10 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 410 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 16 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481899/410-30-55-16 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 450 -SubTopic 20 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.Y.Q1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480102/450-20-S99-1 Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 410 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481931/410-30-50-7 + Details
Name: | us-gaap_AccrualForEnvironmentalLossContingencies
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Recorded amount of the accrual for a material component of an environmental loss contingency. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.Y.Q2) -SubTopic 20 -Topic 450 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480102/450-20-S99-1 + Details
Name: | us-gaap_AccrualForEnvironmentalLossContingenciesComponentAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 450 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483076/450-20-50-4 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 450 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483076/450-20-50-9 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 720 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483359/720-20-50-1 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 460 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 27 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482395/460-10-55-27 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 450 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483076/450-20-50-9 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 450 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483076/450-20-50-4 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 460 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482425/460-10-50-3 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 450 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483076/450-20-50-1 + Details
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Best estimate of the loss exposure for reasonably possible environmental contingencies at an individual site for which no accrual has been recorded. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 410 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481931/410-30-50-10 Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Topic 410 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Subparagraph (d)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481931/410-30-50-10 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 410 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481899/410-30-55-11 + Details
Name: | us-gaap_SiteContingencyLossExposureNotAccruedBestEstimate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=es_NstarElectricCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=es_TheConnecticutLightAndPowerCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=es_PublicServiceCompanyOfNewHampshirePSNHMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=es_MgpSiteAccrualMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=es_EnvironmentalSiteforWhichaRangeisTooEarlytoDetermineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=es_EnvironmentalSitesforWhichaRangeofLossExistsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=es_EvironmentalSiteswithBestEstimateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |