Emerald Eyez said:
BUt, I would need to have a legal document, before I go to the company to ensure that after I reveal my idea to this company, they cannot use it, without my permission. Isn't that what a copyright is to be used for?
No, that's not what copyright is for -- copyright does not protect ideas, only "expressions" of ideas. Copyright cannot protect an idea, or a concept, for a commercial. Copyright can protect the commercial once it's been fleshed out, but the basic idea or concept cannot be protected by copyright.
There really isn't any way of really protecting your idea short of keeping it to yourself. You could ask the company to sign a nondisclosure agreement prior to hearing the idea, so that at least you could potentially sue them for breach of contract if they used your idea without your permission, but it's pretty unlikely that a company would bind themselves in such a way.
So, contact the company, ask for a nondisclosure agreement (if they even take unsolicited submissions in the first place, that is), don't be suprised if they refuse. If they do refuse, then you'll either have to keep the idea to yourself, or trust the company.