Costs Associated with Exit and Restructuring - Summary of Exit and Restructuring Costs Incurred (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Cumulative costs incurred	$ 81	$ 65
Cost incurred	16
Severance, stay bonuses, and other employee-related expenses
Restructuring Cost and Reserve [Line Items]
Cumulative costs incurred	69	54
Cost incurred	15
Obligations for future lease payments
Restructuring Cost and Reserve [Line Items]
Cumulative costs incurred	12	$ 11
Cost incurred	$ 1