Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Income tax benefit	$ (166)	$ (126)
Judicial Ruling [Member] | Tronox Litigation [Member]
Income Tax Disclosure [Line Items]
Income tax benefit	346		$ 346
Unrecognized tax benefits	$ 1,200		$ 1,200
Income tax refunds				$ 881