I Need Professional Advice

Please i need help here. How do i go about selling an idea 2 a company? What is the normal procedure? I know it should be written, but I don’t know how it should be arranged. I have a great idea 4 any of the telecommunication companies to make quick money and unimaginable number of subscribers and still pay relevant role in the building of Nigeria I fear if I just go there, they would steal my idea from me.