Financial Instruments - Additional Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Investments Debt And Equity Securities [Abstract]
Financial instruments including money market funds maturities period	90 days
Maximum maturities period of long-term marketable securities	3 years
Minimum maturities period of long-term marketable securities	1 year
Maximum maturities period of short-term marketable securities	12 months
Minimum maturities period of short-term marketable securities	90 days
Net gain related to forward contracts	$ 3
Derivative Instruments Not Designated as Hedging Instruments, Description of Terms	Our current forward contracts are not designated as hedges and have current maturities of less than 90 days