Income Taxes - Components of Deferred Tax Liabilities and Deferred Tax Assets (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ (322)	$ (251)	$ 3,872