Financial Instruments - Additional Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
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 remaining maturity for short term marketable security	12 months
Minimum maturity for short term marketable security	90 days
Total fair value of marketable securities	$ 68
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