With your audience hooked on your great idea, the next question you need to answer is whether the idea is patentable. Companies typically won't pay someone for an idea that can't be patented. If you have a patent, give them the patent number and a copy of your patent. If your patent is pending, have your patent attorney write a patentability evaluation letter. Never divulge your patent application filing date in a presentation. Sharing this information before you receive your patent can greatly compromise your idea's protection.
If you haven't filed for a patent but know your idea is patentable, get a confidentiality agreement signed before disclosing your idea. If your idea isn't patentable, you can still present your idea; however, you run the risk of someone stealing it without giving you any compensation. And unfortunately, this type of "theft" is perfectly legal.