I hate to be the voice of doom here, but there is about ....oh ..... no chance whatsoever of them picking up your idea. Unless you're an artist and are insanely awesome. If you're a writer......
Sorry, but Marvel wouldn't do a new idea if f*cking Grant Morrison pitched it to them. Hell, if Dan Brown or J.K. Rowling wanted to, they'd tell them to buzz of. Even if Shakespeare rose from the dead to write a comic, they would keep on slogging away at the same ol' books with the same ol' creators.
They are in the business of superheroes. More accurately, they are in the business of THEIR superheroes. More accurately, they are in the business of their superheroes as written by Brian Michael Bendis.
It's a tough world. Try Dark Horse, they seem more receptive (and they have a New Recruits drive every year).
P.S. I know I'm a jerk. But by saying this I've added to your karmic balance and actually HELPED you get your pitches accepted just to prove me wrong! You're welcome.