But, what the hell....

Does anybody know the process they go through to make a video game? I think I worded that wrong, but the reason I'm asking is, I have an idea that I started thinking about as a movie, but the more I think about it, the more I think it would work great as a Silent Hill or Resident Evil type game. So, what I'm wondering is if these companies actually take ideas from outside sources, or if the ideas come only from within the production companies themselves. Like I said, I'm doubting anyone here knows anything about this, but I figured it's worth a shot.