Income Taxes - Schedule of Income Taxes Calculated on Income before Income Taxes and Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income before provision for income taxes	$ 553	$ 661	$ 526
Federal statutory income tax rates	21.00%	21.00%	21.00%
Income taxes, at statutory income tax rate	$ 116	$ 139	$ 110
State income tax, net of federal income tax	23	27	13
Excess deferred tax amortization	(25)	(25)	(26)
ITC amortization	(8)	(6)	(9)
AFUDC-equity	(4)	(7)	(9)
Production Tax Credits	(15)	(6)	0
Other Tax credits	(4)	(3)	(3)
Other	4	2	4
Total income tax expense	$ 87	$ 121	$ 80
Income tax expense as a percent of income before income taxes	15.70%	18.30%	15.20%