Exit and Disposal Costs - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring And Related Activities [Abstract]
Severance expense	$ 38	$ 18	$ 55
Accrued severance costs paid	40	48	$ 52
Charges in connection with vacated office space	73	14
Accrued severance costs	4	6
Accrued liabilities for exit costs	$ 85	$ 28
Expected period for all payments for severance cost	Accrued severance costs are expected to be paid in 2019