If the idea is totally outside of your field of work, and the clients' field of work, yeah that's a little weird. If you and the client are in the same field, it's not weird at all. Ideas happen all the time. There are probably other people in your field who have the same idea and will be competing with you. If you want to mainline this, listen to a lot of pitches from startup CEOs. For any possible new idea there will be a few dozen startups trying to raise money all of a sudden within a few weeks. Great ideas are common, execution is everything!