unamortized deferred compensation expense , which includes both options and rsus , amounted to $ 378 million as of december 31 , 2015 , with a remaining weighted-average amortization period of approximately 2.1 years . employee share purchase plan united states the company has an employee share purchase plan that provides for the purchase of a maximum of 7.5 million shares of the company's ordinary shares by eligible u.s . employees