Some really good perspectives here. All a great. If you are determined to leverage a large company, you can try try this approach. I brought several small companies into IBM with big ideas and a couple leveraged the IBM machine to build sizable companies in a similar way.
First, find people who will pay for your idea. Research all sides of the solution. What other technologies can be incorporated in your idea. If your idea requires other software components, professional services, and hardware, you have more points of leverage. Approach a large company with your idea and back that up with a list of people who will pay for a delivered solution. If you present a solid case with paying customers, most large companies, like IBM, have people who can make an investment and prime a solution. Of course, there are many things for you to worry about here, but it can be done; I lived it.
This only works in the enterprise software business. Since we do not know what your idea is, it is difficult to be more helpful. I offer this up because anything is possible. :)
Best of luck.