Income Taxes - Additional Information (Detail) - USD ($)		12 Months Ended
	Sep. 14, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Taxes [Line Items]
Federal statutory tax rate		21.00%	21.00%	21.00%
Regulatory liability due to obligation to transfer tax rate reduction expense benefit		$ 23,000,000	$ 7,000,000
Provision for income taxes		87,000,000	121,000,000	$ 80,000,000
General business credit		$ 324,000,000
Deferred tax general business credits expiration date		2027-2043
Investment tax credits		$ 266,000,000
Investment tax credit expiration date		2034 and 2043
Uncertain tax positions		$ 10,000,000	9,000,000	6,000,000	$ 9,000,000
Unrecognized tax benefits decreased				0
Pre-tax charges (benefits)		0	0	0
Interest accrued		0	0	0
Penalties		$ 0	0	0
Statutes of limitations		3 years
Income tax examination period		1 year
Decrease in current income tax expense			(59,000,000)
Federal [Member] | R&D Tax Credits [Member]
Income Taxes [Line Items]
Uncertain tax positions		$ 10,000,000	$ 9,000,000
Unrecognized tax benefits decreased				$ 5,000,000
Florida [Member]
Income Taxes [Line Items]
Florida corporate income tax rate	4.46%	5.50%		3.53%
Regulatory liability due to obligation to transfer tax rate reduction expense benefit				$ 4,000,000