How I can protect an idea without a patent filed?

Write a description of your idea on a piece of paper and mail it to yourself. When mail arrives to keep it closed.

Develop an idea

Recalling that it would be difficult to sue someone for stealing an idea. One idea is just that - to be something else you need details of how to develop, so one thing to have an idea or concept of something, but if you can not afford to develop this idea into a reality after being all that remains - an idea.

Take this very simplistic example.  

Suppose I have an idea of a bagless vacuum cleaner, and I approached Mr. Dyson, I say that I have a great idea for a new vacuum - why not make them without a bag. Well, assuming that Mr. Dyson goes on and I can not sue him for stealing my idea, because at the end of the day. 

Mr. Dyson is that then took the idea and made ​​it a reality - came up with the design, technology, etc to make this idea a reality. For me to say he stole my idea would have to prove the technology, design and so was my idea too. Hope I'm doing makes sense.