Income Taxes - Schedule of Income Tax Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Current income taxes, Federal	$ 2	$ 84	$ (13)
Current income taxes, State	0	25	(3)
Deferred income taxes, Federal	36	(19)	105
Deferred income taxes, State	34	5	38
Investment tax credits amortization	(4)	(8)	(6)
Total income tax expense	$ 68	$ 87	$ 121