How to give an idea for something to like Chevy or ford or something?

I have an idea that I know would make a lot of money for them but I want to tell them, not anyone else about it, and should I try and patent it first?

Ever seen the movie "Flash of Genius"? Therein, lies your Answer.

Put your idea into words and google it with the word "patent" chances are someone already invented it. Pretty hard to be original on a planet with 7 billion people on it.

Patent it first. The first step to a patent is to describe the idea or item on paper. Draw a diagram of it and mail it to yourself. That way, the postmark is your guarantee that you were the first to think of it. Do not open the letter. After you get the patent, then go to Chevy or Ford. Then they will steal it from you like they do everything else.