XML 77 R62.htm IDEA: XBRL DOCUMENT v3.24.0.1
Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
 1 Months Ended 12 Months Ended
Aug. 31, 2022
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2017
Income Taxes [Line Items]            
Statutory Federal Income Tax Rate   21.00% 21.00% 21.00%    
Regulatory Liability   $ 47.9 $ 51.9      
Regulatory liability, expected flow back to customers         $ 47.1  
Regulatory liability, expected pass back to ratepayers   1.3       $ 1.8
Net Operating Loss Carryforwards Utilized For Income Taxes     1.4      
Deferred tax assets, operating loss carryforwards, federal   4.4        
Percentage of alternate minimum tax 15.00%          
Number of years used for calculating adjusted financial statement income 3 years          
Adjustment financial statement income $ 1.0          
FederalTaxCreditsToOffsetCurrentTaxes     1.7      
Income Tax Related Liabilities            
Income Taxes [Line Items]            
Regulatory Liability   38.6 $ 41.0     $ 48.9
Gas Ratepayers | Massachusetts And Maine [Member]            
Income Taxes [Line Items]            
Regulatory liability, expected flow back to customers   $ 9.3        
Tax Year 2018            
Income Taxes [Line Items]            
Statutory Federal Income Tax Rate           21.00%