Employee Benefit Plans and Equity Compensation Plan (Schedule of Defined Benefit Plan Amounts Recognized in Regulatory Assets) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets, pension and other postretirement benefit plans, net unamortized gain (loss) arising during the period, net of tax	$ (27)	$ 95	$ (39)
Regulatory assets, amortization of actuarial gain (loss), pension and other postretirement benefit plans, net of tax	(11)	(1)	(5)
Regulatory assets, current year prior service cost, pension and other postretirement benefit plans, net of tax	1	0	0
Regulatory assets, total recognized in regulatory assets, pension and other postretirement benefit plans, net of tax	(37)	94	(44)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets, pension and other postretirement benefit plans, net unamortized gain (loss) arising during the period, net of tax	2	(41)	(6)
Regulatory assets, amortization of actuarial gain (loss), pension and other postretirement benefit plans, net of tax	3	0	0
Regulatory assets, current year prior service cost, pension and other postretirement benefit plans, net of tax	0	0	0
Regulatory assets, total recognized in regulatory assets, pension and other postretirement benefit plans, net of tax	$ 5	$ (41)	$ (6)