Financial Instruments - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Financial instruments including money market funds maturities period		90 days		90 days
Maximum remaining maturity for short-term marketable securities		12 months		12 months
Minimum maturities of short-term marketable securities		90 days		90 days
Net loss related to forward contract	$ (3)		$ (3)
Cost method investments		$ 12		$ 12