There is no market for ideas: they're the easy part. Writing them convincingly is what takes time and skill.
Every writer has more ideas than they can keep up with: it's highly unlikely that anyone would find a writer interested in writing up their idea unless they were a celebrity, or knew something that a celebrity would rather they didn’t share.
"From an idea by", and similar acknowledgements, don’t come about when some guy rocks up to a producer, says, "Hey, I've got a fantastic idea for a film!" and bingo, the film is made. They happen when someone has written a treatment, novel, screenplay or story that is good, but not strong enough to be published or produced as it is. Other people work on it and make it marketable; in so doing it’s removed from its original conception, but it still warrants that acknowledgement.
Literary agents and publishers don't deal in ideas, just in finished works (or part-finished works for non-fiction). Don't submit your ideas to anyone: you'll be wasting your time and theirs. Submit your writing instead. An editor or agent who responds with interest to ideas alone is very likely to be a scammer, and more interested in taking your money than in selling your project. And we know how we feel about them.