Income Taxes - Additional Information (Detail) - USD ($)		12 Months Ended
	Sep. 14, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Federal statutory tax rate		21.00%	21.00%	21.00%
Federal statutory tax rate		4.50%	5.50%
Provision for income taxes		$ 80,000,000	$ 82,000,000	$ 77,000,000
Deferred tax assets expiration date		2032 and 2037
General business credit		$ 286,000,000
Deferred tax general business credits expiration date		2027 and 2041
Investment tax credits		$ 264,000,000
Investment tax credit expiration date		2034 and 2041
Uncertain tax positions		$ 6,000,000	9,000,000	9,000,000	$ 8,000,000
Unrecognized tax benefits decreased		0	2,000,000
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
Federal [Member]
Income Taxes [Line Items]
Federal and Florida net operating losses (NOL's) carryforward		$ 312,000,000
Federal [Member] | R&D Tax Credits [Member]
Income Taxes [Line Items]
Uncertain tax positions		6,000,000	9,000,000
Unrecognized tax benefits decreased		$ 5,000,000	$ 2,000,000
Florida [Member]
Income Taxes [Line Items]
Federal statutory tax rate	4.46%	3.53%
Regulatory liability due to obligation to transfer tax rate reduction expense benefit		$ 4,000,000
Federal and Florida net operating losses (NOL's) carryforward		$ 83,000,000