Financial Instruments and Fair Value Measurements - Summary of Undesignated Financial Instruments Exercised and Realized and Unrealized Gains (Losses) in Foreign Currency and Derivative Gains (Losses) Net (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Exercised contracts | Contract	17	11	48	33
Realized gains (losses) on the matured, expired or settled contracts	$ 1	$ 2	$ (7)	$ 11
Unrealized gains (losses) on the change in fair value of outstanding contracts	$ 6	$ (12)	$ 23	$ (45)