This isn't something you actually want.
For the US, copyright law says the following:
In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work.
You can't copyright an idea, for good reason. I'd be willing to bet that no matter what your idea is, it's not purely original. Your idea almost certainly contains what could be considered derivative works at one level or another. Your world has mages that summon ice cream? Sorry, that's simply a derivative of any idea containing magic user summoning food items, which themselves were derivative ideas of fictional characters performing impossible things, which is simply a derivative (due to the deliberately opposite nature) of a normal character doing a normal thing.
It gets ridiculous and meaningless quite quickly when you try to protect something as intangible as an idea.
So, no, you can't protect your idea. But that's not where people make their living as authors or story tellers. It's in the implementation. The words you use to tell the story and the way it all comes together is something you can protect. Ideas are worthless without implementation.
Ultimately, you'd be better off sharing the ideas you have for your world, especially on a site like Worldbuilding, because what you're going to get in return is a whole bunch more free ideas and refinements to your original idea.