Income Tax - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax [Line Items]
Reserve for uncertain tax positions	$ 0	$ 0	$ 0
Earliest year open to examination	2007
Federal [Member]
Income Tax [Line Items]
U.S. federal tax loss carryforwards ("NOL")	$ 1,400,000,000
Permanently lost amount of U.S. federal tax loss carryforwards ("NOL")	$ 386,000,000
Tax loss carryforwards expiration year	2034