Ideas are the easy part. It’s turning them into codes/maps/models/textures/sounds that is hard. Hundreds or thousands of hours of unpaid work is a pretty good deterrent against people stealing your ideas.
If you want to attract people to your mod, you almost certainly want something that shows you are serious about it, not just another guy with a “great idea” who other people to do all the work.
If you expect to have a role in the mod team, you should show off your work. If you are a coder, code some of the gameplay mechanics. If you are a modeler, show off some killer models. If you are a mapper, make a map.
If all you bring to the mod is the idea, your chances of getting a team together are very slim.