What is the difference between an idiom and a hyperbole?

With an idiom, the meaning of the group of Words has a moral meaning. Like the saying, a leopard can't get rid of its spots, you can't get rid of your total body image. A hyperbole is an exageration used for effect. It's just an exageration, it doesn't have a special meaning in it. "Her brain is the size of a pea" is a perfect example.