Components of Gas Inventory (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	$ 1.0	$ 0.6
Liquefied Natural Gas & Other
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	0.1	0.1
Natural Gas
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	0.5	0.2
Propane
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	$ 0.4	$ 0.3