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Regulatory Matters (Additional Information) (Details 1) $ in Millions													3 Months Ended	6 Months Ended	12 Months Ended
	Jul. 16, 2024 USD ($)	Jun. 28, 2024 USD ($)	Nov. 27, 2023 USD ($)	Nov. 01, 2023 USD ($)	Aug. 17, 2023 USD ($)	Jul. 27, 2023 USD ($)	Jul. 26, 2023 USD ($)	Dec. 30, 2022 USD ($)	Aug. 19, 2022 USD ($)	Aug. 24, 2021 USD ($)	Nov. 30, 2020 USD ($)	Jun. 25, 2019	Mar. 31, 2023 USD ($)	Jun. 30, 2024 USD ($) MW	Dec. 31, 2023 USD ($)	Dec. 31, 2022	May 31, 2024 USD ($)	Oct. 31, 2023 USD ($)	Aug. 30, 2023 MW	May 31, 2023 USD ($)	Nov. 30, 2022 USD ($)	Oct. 31, 2022 USD ($)	Oct. 07, 2022 USD ($)	May 25, 2022 MW	May 07, 2021 MW	Feb. 10, 2020 MW	May 31, 2019 MW	Jul. 31, 2018 MW MWh	Jun. 30, 2017 MW MWh
Regulatory Asset [Line Items]
Recover costs of repairing damage													$ 4.8
Approved commitments for purchasing assets								$ 1.0
Contract with Customer, Right to Recover Product, Total													4.8
Remuneration Percentage												2.75%				2.25%
Termination agreements														$ 1.1
Public Infrastructure Offering [Member]
Regulatory Asset [Line Items]
Approved commitments for purchasing assets								0.5
Electric Vehicle Supply Equipment [Member]
Regulatory Asset [Line Items]
Approved commitments for purchasing assets								0.3
Marketing And Outreach [Member]
Regulatory Asset [Line Items]
Approved commitments for purchasing assets								$ 0.2
Fitchburg Gas Company
Regulatory Asset [Line Items]
Public utilities interim increase decrease amount					$ 10.9
Increase (decrease) in annual revenue					4.2
Regulatory assets approved increase in revenue due to be recovered					$ 6.7													$ 6.4				$ 4.5
Approved annual increase in rates		$ 10.1
Increase in cost		$ 4.9
Percentage of approved return on equity		9.40%
Percentage of approved return on equity, reflecting on equity		52.00%
Percentage of approved return on equity, reflecting on debt		48.00%
Granite State
Regulatory Asset [Line Items]
Increase (decrease) in annual revenue						$ 1.0			$ 0.3	$ 0.1	$ 1.3
Spending cap											14.6
Fitchburg Grid Modernization
Regulatory Asset [Line Items]
Regulatory assets approved increase in revenue due to be recovered																	$ 1.3			$ 1.0
Amount of replacement investments approved by regulatory authority																					$ 11.2
Purchase commitments for data sharing platform investments											2.3
Order providing cost		$ 1.6
Fitchburg Gas And Electric Light Company [Member]
Regulatory Asset [Line Items]
Increase (decrease) in annual revenue			$ 3.5	$ 3.6			$ 3.1
Increase in cost		$ 2.2
Percentage of approved return on equity		9.40%
Percentage of approved return on equity, reflecting on equity		52.00%
Percentage of approved return on equity, reflecting on debt		48.00%
Power generation capacity \| MWh																													9,450,000
Facility power capacity to be procured in the future \| MW																			400
Fitchburg Gas And Electric Light Company [Member] \| Minimum [Member]
Regulatory Asset [Line Items]
Facility power capacity to be procured in the future \| MW														200
Fitchburg Gas And Electric Light Company [Member] \| Maximum [Member]
Regulatory Asset [Line Items]
Facility power capacity to be procured in the future \| MW														2,400
Fitchburg Gas And Electric Light Company [Member] \| Offshore Wind Energy
Regulatory Asset [Line Items]
Remuneration Percentage												2.75%
Power generation facility \| MW																										400		400	1,600
Facility power capacity to be procured in the future \| MW														5,600					5,600
Fitchburg Gas And Electric Light Company [Member] \| Offshore Wind Energy \| Second Solicitation [Member]
Regulatory Asset [Line Items]
Power generation facility \| MW																									1,600		800
Fitchburg Gas And Electric Light Company [Member] \| Offshore Wind Energy \| Third Solicitation [Member]
Regulatory Asset [Line Items]
Power generation facility \| MW																								1,200
Fitchburg Gas And Electric Light Company [Member] \| Mayflower Wind Energy \| Third Solicitation [Member]
Regulatory Asset [Line Items]
Power generation facility \| MW																								400
Fitchburg Gas And Electric Light Company [Member] \| Qualified Clean Energy
Regulatory Asset [Line Items]
Power generation capacity \| MWh																												9,554,940
Subsequent Event [Member] \| Fitchburg Gas Company
Regulatory Asset [Line Items]
Increase in cost	$ 0.9
Subsequent Event [Member] \| Fitchburg Gas And Electric Light Company [Member]
Regulatory Asset [Line Items]
Increase in cost	$ 0.8
Major Storm Cost Reserve Recovery [Member]
Regulatory Asset [Line Items]
Recover costs of repairing damage															$ 3.7
Carrying costs															0.2
Contract with Customer, Right to Recover Product, Total															3.7
Additional Carrying Costs															$ 0.2
Storm Cost Deferral Petition [Member]
Regulatory Asset [Line Items]
Carrying costs													1.4
Additional Carrying Costs													$ 1.4
Track One \| Fitchburg Grid Modernization
Regulatory Asset [Line Items]
Amount of capital expenditure approved by regulatory authority																							$ 9.3
Track Two \| Fitchburg Grid Modernization
Regulatory Asset [Line Items]
Amount of capital expenditure approved by regulatory authority											$ 1.5