Income Taxes - Additional Information (Detail) - USD ($)		3 Months Ended	12 Months Ended
	Sep. 12, 2019	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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			$ 82,000,000	$ 77,000,000	$ 81,000,000
Deferred tax assets expiration date			2032 and 2037
General business credit		$ 242,000,000	$ 242,000,000
Deferred tax general business credits expiration date			2027 and 2040
Investment tax credits		222,000,000	$ 222,000,000
Investment tax credit expiration date			2034 and 2040
Uncertain tax positions		9,000,000	$ 9,000,000	9,000,000	8,000,000	$ 8,000,000
Unrecognized tax benefits decreased			2,000,000
Pre-tax charges (benefits)			0	0	0
Interest accrued		0	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		340,000,000	$ 340,000,000
Federal [Member] | R&D Tax Credits [Member]
Income Taxes [Line Items]
Uncertain tax positions		9,000,000	$ 9,000,000	$ 9,000,000
Unrecognized tax benefits decreased		2,000,000
Florida [Member]
Income Taxes [Line Items]
Federal statutory tax rate	5.50%		4.46%
Federal and Florida net operating losses (NOL's) carryforward		$ 88,000,000	$ 88,000,000