Hi Nick,
Nope. Ideas cannot be protected by copyright. Or any other 'protection' registration like trademarks, etc.
What you need is a good business attorney. Get a 'non-disclsoure' or 'non-compete' agreement prepared. Get it signed by your prospective investor before you show them the idea. This is just slightly better than nothing. :)
This is one of those 'catch 22' situations. You will have to 'trust' somebody, and hope for the best. Prepare yourself. Create some kind of record that the idea is yours, that it existed BEFORE you showed it to somebody. Unfortunately, your 'word' is seldom enough to convince a judge - they like proof. And if somebody 'steals' your idea, that is likely the only way you have to make any claims.
You might be able to obtain protections under the patent laws, but my read on that is that you must actually have a model or design. Again, a good attorney is the best advisor for you.
Good Luck!