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Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	9 Months Ended		12 Months Ended
	Aug. 31, 2022	Dec. 31, 2020	Mar. 31, 2022	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2017
Income Taxes [Line Items]
Corporate federal income tax				21.00%	21.00%
Regulatory liability, expected flow back to customers							$ 47.1
Regulatory liability, expected pass back to ratepayers				$ 1.0
Net Operating Loss Carryforwards Utilized For Income Taxes						$ 2.4
Deferred tax assets, operating loss carryforwards, federal				$ 5.8
Percentage of employment retention credit			50.00%
Employment retention duties capacity			100.00%
Percentage of alternate minimum tax	15.00%
Adjustment financial statement income	$ 1,000.0
Number of years used for calculating adjusted financial statement income	3 years
Consolidated Appropriations Act 2021 [Member]
Income Taxes [Line Items]
Percentage of employment retention credit		70.00%
Employment retention duties capacity		100.00%
Minimum
Income Taxes [Line Items]
Average Rate Assumption Method estimated flow back period				15 years
Maximum
Income Taxes [Line Items]
Average Rate Assumption Method estimated flow back period				20 years
Gas Ratepayers | Massachusetts And Maine [Member]
Income Taxes [Line Items]
Regulatory liability, expected flow back to customers				$ 5.4
Tax Year 2018
Income Taxes [Line Items]
Corporate federal income tax							21.00%	21.00%

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible domestic operating loss carryforwards. Excludes state and local operating loss carryforwards.

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Employment Retention Duties Capacity.

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