Employee Benefit Plans and Equity Compensation Plan (Amounts Recognized in Regulatory Assets) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ 126	$ 164
Prior service cost	1	0
Total	127	164
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	(41)	(46)
Prior service cost	0	0
Total	$ (41)	$ (46)