Income Taxes - Schedule of Income Tax Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Current income taxes, Federal	$ 84	$ (13)	$ 48
Current income taxes, State	(25)	(3)	4
Deferred income taxes, Federal	19	105	24
Deferred income taxes, State	5	38	13
Investment tax credits amortization	(8)	(6)	(9)
Total income tax expense	$ 87	$ 121	$ 80