How you send in a commercial idea to a big company?

You are asking a loaded question. Large corporations normally hire ad agencies to create and place their TV and radio commercials. If you just send your idea directly to the corporation and they like it, they will most likely send it to their agency, which will probably leave you out in the cold. The tactic I would use is research who their agency on record is and propose your idea to the agency as an independent consultant. Make sure you have an agreement so you get paid for your commercial so you don't give your idea away for free. If you have a dynamite idea, the agency may choose to retain you for future commercials. In either option it is wise to copyright the idea