Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Tax reform legislation income tax benefit	$ 5
Income tax benefit	(256)	$ 425	$ (507)	$ 366
Tronox Litigation [Member] | Judicial Ruling [Member]
Income Tax Disclosure [Line Items]
Income tax benefit			346		$ 346
Unrecognized tax benefits	$ 1,200		$ 1,200		$ 1,200
Income tax refunds						$ 881