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Regulatory Matters (Additional Information) (Details 1) $ in Millions														3 Months Ended	9 Months Ended	12 Months Ended
	Nov. 01, 2024 USD ($)	Oct. 04, 2024 USD ($)	Sep. 11, 2024 USD ($)	Jul. 16, 2024 USD ($)	Jun. 28, 2024 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 ($)	Sep. 30, 2024 USD ($) MW	Dec. 31, 2023 USD ($)	Dec. 31, 2022	Oct. 31, 2024 USD ($)	Sep. 06, 2024 MW	Jul. 15, 2024 USD ($)	May 31, 2024 USD ($)	Oct. 31, 2023 USD ($)	Aug. 30, 2023 MW	May 31, 2023 USD ($)	Nov. 30, 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 MWh MW	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												$ 3.5				$ 6.4
Approved annual increase in rates					$ 10.1
Increase in cost				$ 0.9	$ 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%
Fitchburg Gas Company \| Minimum [Member]
Regulatory Asset [Line Items]
Regulatory assets approved increase in revenue due to be recovered																				$ 4.0
Fitchburg Gas Company \| Maximum [Member]
Regulatory Asset [Line Items]
Regulatory assets approved increase in revenue due to be recovered																				$ 6.4
Granite State
Regulatory Asset [Line Items]
Increase (decrease) in annual revenue		$ 3.0					$ 1.0			$ 0.3	$ 0.1	$ 1.3
Spending cap		$ 29.9										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	$ 0.5		$ 3.5					$ 3.1
Increase in cost				$ 0.8	$ 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				2,678				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
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