Dr Strange is probably going to make more than Ant-Man, but 1 billon WW looks really far away.
If we follow most Superhero movies, the maximum box office WW is around 700million-800millon, best case scenario
The only exceptions are Batman movies (because Batman), and Avenger kinda movies (1,2 and Civil War). You can match there Iron Man3, but Strange don't have such a huge popularity right now