Is it easier to write a novel, then turn it into a movie? Or go write into writing a screenplay?

I have a great idea for a movie/novel, its an idea that has not yet
been made into a movie or novel. So I just dont know where to start. I
think i can put more detail and explain the storyline better if i put
it into a novel. Once i finish, write a screen play out of it? is that
something anyone has herd of?