Income Taxes - Additional Information (Detail) - USD ($)			12 Months Ended
	Jan. 01, 2018	Sep. 27, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Federal statutory tax rate			35.00%	35.00%	35.00%
Deferred tax assets			$ 199,000,000	$ 316,000,000
Deferred tax liabilities			1,024,000,000	1,723,000,000
Asset expensing, uncertainty provisional percentage		100.00%
Provision for income taxes			197,000,000	152,000,000	$ 166,000,000
Change in net deferred taxes offset to regulatory tax liability			$ 755,000,000
Deferred tax assets expiration date			2033 and 2037
General business credit			$ 23,000,000
Deferred tax general business credits expiration date			2028 and 2037
Uncertain tax positions			$ 8,000,000	7,000,000	0	$ 0
Pre-tax charges (benefits)			0	0	0
Interest accrued			0	0	$ 0
Penalties			$ 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			$ 345,000,000
Federal [Member] | R&D Tax Credits [Member]
Income Taxes [Line Items]
Uncertain tax positions			8,000,000	$ 7,000,000
Florida [Member]
Income Taxes [Line Items]
Federal and Florida net operating losses (NOL's) carryforward			$ 273,000,000
Subsequent Event [Member]
Income Taxes [Line Items]
Federal statutory tax rate	21.00%
Asset expensing	100.00%