Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Oct. 31, 2013
Storm Restoration Cost Recovery [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Minimum cost recovery period	12 months
Replenishment reserve for recovery of cost		$ 56
Capital Cost Recovery for Early Retired Assets [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Settlement agreement cost recovery period	15 years