Income Taxes - Components of Income Tax Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Current tax benefit (expense)	$ 0	$ 3	$ 4	$ (4)
Deferred tax benefit (expense)	3	(1)	2	0
Total income tax benefit (expense)	$ 3	$ 2	$ 6	$ (4)