Exit and Disposal Costs - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
Restructuring Cost And Reserve [Line Items]
Severance expense			$ 39
Severance costs paid as part of previously announced cost reduction program			39
Accrued severance cost	$ 6		$ 6	$ 6
Expected period for payment for severance cost			We expect to pay in the fourth quarter of 2018
General and Administrative Expenses
Restructuring Cost And Reserve [Line Items]
Charges in connection with vacated office space	$ 57	$ 11