Assuming users are not on both mobile and desktop, then the desktop is around 100 million (DAU less Mobile DAUs):

Daily active users (DAUs) – DAUs were 1.18 billion on average for September 2016, an increase of 17% year-over-year. Mobile DAUs – Mobile DAUs were 1.09 billion on average for September 2016, an increase of 22% year-over-year.