Where does Wayne's money come from?

How many hours does Wayne's day have that he can do millions or billions of dollars worth of actual work while still playing dress-up at night?

Or does his money come from short-changing and underpaying his employees, while hiking the prices for his customers? Or does it come from using speculation and investment to make sure he gets rich off other people being underpaid and overcharged?

How can he be a philanthropist when all his money comes from fleecing other people?