Income Taxes - Changes in VA for Deferred Tax Assets (Detail) - Valuation Allowance for Deferred Tax Assets [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Income Tax [Line Items]
Balance at beginning of period	$ 200	$ 335	$ 336
Addition due to the Combination	836
Charged to costs and expenses	250	(32)	15
Charged to other accounts	21	(103)	(16)
Balance at end of period	$ 1,307	$ 200	$ 335