Amount of contractual obligation, including, but not limited to, long-term debt, lease obligation, purchase obligation, and other commitments.

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-Topic 235
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Amount of capital expenditure approved by regulatory authority

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Budget for Additional investment

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Expenses associated with the program excluded from the revenue requirement as per order and adjusted increase amount will result in reasonable rates

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Facility Power Capacity

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Public utilities approved increase amount of annual revenue to recover eligible capital investments

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recover deferred costs

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Regulatory Matters - Additional Information (Detail) $ in Millions																									1 Months Ended	3 Months Ended
	May 01, 2023 USD ($)	Apr. 15, 2023 USD ($)	Feb. 14, 2023 USD ($)	Dec. 30, 2022 USD ($)	Nov. 02, 2022 USD ($)	Sep. 22, 2022 USD ($)	Aug. 19, 2022 USD ($)	Jul. 28, 2022 USD ($)	Jul. 20, 2022 USD ($)	Jul. 15, 2022 USD ($)	Jun. 08, 2022 USD ($)	May 12, 2022 USD ($)	May 03, 2022 USD ($)	May 01, 2022 USD ($)	Jan. 31, 2022 USD ($)	Nov. 02, 2021 USD ($)	Aug. 24, 2021 USD ($)	Mar. 01, 2021 USD ($)	Nov. 30, 2020 USD ($)	Apr. 01, 2020 USD ($)	Mar. 31, 2020 USD ($)	Feb. 28, 2020 USD ($)	Jul. 31, 2018 MWh MW	Jun. 30, 2017	Mar. 31, 2020 USD ($)	Mar. 31, 2022 USD ($)	Jun. 30, 2027 MWh MW	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Nov. 30, 2022 USD ($)	Oct. 31, 2022 USD ($)	Oct. 07, 2022 USD ($)	May 31, 2022 MW	May 27, 2022 USD ($)	May 07, 2021 MW
Regulatory Asset [Line Items]
Approved annual increase in rates																				$ 3.6	$ 4.6
Increase in annual base rate																				3.60%
Requested annual increase in rates														$ 2.1
Approved annual increase in rates																									$ 3.7
Deferred cost related to exogenous event																												$ 1.1
Budget For EV program				$ 1.0
Program Segment spendings description				The Company may shift spending between program segments and between years over the five-year term of its program, subject to a 15 percent cap. Any spending above the approved EV program budget or above the 15 percent cap for each program segment is not eligible for targeted cost recovery through the GMF
Other Restructuring
Regulatory Asset [Line Items]
Cost recovery period, years																												2 years
Offshore Wind Energy
Regulatory Asset [Line Items]
Power generation facility \| MW																											1,600
Northern Utilities Inc
Regulatory Asset [Line Items]
Percentage of approved return on equity													9.20%
Percentage of approved return on equity, reflecting on equity													52.00%
Percentage of approved return on equity, reflecting on debt													48.00%
Approved annual increase in rates	$ 11.8		$ 1.2								$ 1.6		$ 6.3
Increase in annual base rate	9.40%
Public utilities approved increase amount of annual revenue to recover eligible capital investments								$ 1.3
Northern Utilities Inc \| Settlement Agreement [Member]
Regulatory Asset [Line Items]
Approved annual increase in rates									$ 6.1
Northern Utilities Inc \| Arrearage Management Program [Member]
Regulatory Asset [Line Items]
Expenses associated with the program excluded from the revenue requirement as per order and adjusted increase amount will result in reasonable rates												$ 5.9
Northern Utilities Inc \| New Hampshire
Regulatory Asset [Line Items]
Percentage of approved return on equity										9.30%
Percentage of approved return on equity, reflecting on equity										52.00%
Percentage of approved return on equity, reflecting on debt										48.00%
Threshold amount that will be allowed to adjust distribution rates upward or downward during the term of stay out period										$ 200,000.0
Fitchburg Gas and Electric Light Company
Regulatory Asset [Line Items]
Increase (decrease) in annual revenue					$ 3.1											$ 1.6
Percentage of approved return on equity															9.70%
Percentage of approved return on equity, reflecting on equity															52.45%
Percentage of approved return on equity, reflecting on debt															47.55%
Power generation capacity \| MWh																											9,450,000
Remuneration Percentage				2.25%
Revenue impact threshold															$ 0.1
Fitchburg Gas and Electric Light Company \| Offshore Wind Energy
Regulatory Asset [Line Items]
Power generation capacity \| MW																							400
Remuneration Percentage																							2.75%	2.75%
Fitchburg Gas and Electric Light Company \| Offshore Wind Energy \| Second Solicitation [Member]
Regulatory Asset [Line Items]
Power generation capacity \| MW																																	1,600		1,600
Fitchburg Gas and Electric Light Company \| Qualified Clean Energy
Regulatory Asset [Line Items]
Power generation capacity \| MWh																							9,554,940
Fitchburg Gas Company
Regulatory Asset [Line Items]
Percentage of approved return on equity																						9.70%
Percentage of approved return on equity, reflecting on equity																						52.45%
Percentage of approved return on equity, reflecting on debt																						47.55%
Regulatory assets approved increase in revenue due to be recovered														$ 3.3																	$ 4.5			$ 0.4
Recovery of deferred costs		$ 1.0
Approved annual increase in rates															$ 1.1			$ 0.9
Approved annual increase in rates																										$ 0.9
Apporved annual decrease in rates																										$ 0.2
Revenue impact threshold																						$ 40,000.0
Fitchburg Gas Company \| Track One [Member]
Regulatory Asset [Line Items]
Amount of capital expenditure approved by regulatory authority																																$ 9.3
Fitchburg Gas Company \| Track Two [Member]
Regulatory Asset [Line Items]
Budget for Additional investment																														$ 1.5
Budget for replacement investments																														11.2
Amount of replacement investments approved by regulatory authority																														$ 2.3
Granite State
Regulatory Asset [Line Items]
Increase (decrease) in annual revenue							$ 0.3										$ 0.1		$ 1.3
Spending cap																													$ 14.6
With Effect From First January Two Thousand And Twenty Three [Member]
Regulatory Asset [Line Items]
Public utilities interim increase decrease amount						$ 0.7
With Effect From First March Two Thousand And Twenty Three [Member] \| Fitchburg Gas Company
Regulatory Asset [Line Items]
Public utilities interim increase decrease amount						0.7
Recover Deferred Costs						$ 1.2
Public Infrastructure Offering [Member]
Regulatory Asset [Line Items]
Budget For EV program				$ 0.5
Electric Vehicle Supply Equipment [Member]
Regulatory Asset [Line Items]
Budget For EV program				0.3
Marketing And Outreach [Member]
Regulatory Asset [Line Items]
Budget For EV program				$ 0.2