First off, story pitches are only accepted after you’ve been invited to pitch by an editor and you’ve signed a non-disclosure agreement. You can’t send unsolicited story ideas to Marvel or DC. They legally can’t accept them. I know it’s frustrating, but that’s the simple truth. You have to get on their radar and be asked to pitch.
Once you’ve crossed that crucial hurdle, you’ll usually be asked to pitch on a specific project, rather than just pitching whatever you want. Every editor is a bit different, but the initial concept is usually a 1-2 page overview of your concept and what makes it tick. I cover this kind of pitch on my website here:
The example I have at that link is for a creator-owned concept, but the overall approach is similar for a work-for-hire project. I want to get the editor excited about the possibilities at this stage and hit the high points of the story without getting bogged down in minutiae.
If the editor likes the pitch, they’ll usually ask for a more detailed story breakdown, outlining the major story beats for each issue in the first arc or for the mini-series as a whole. There’s no set length for this, but mine are usually about 2/3 of a page per issue, so a six issue mini-series breakdown would run approximately 4 pages.
If you’re using established characters you probably won’t have to explain who they are to the editor, but if you’re adding new elements or bringing back something obscure those may require extra explanation.
From there, assuming it’s approved, you’ll move on to scripting. If this is your first major project for Marvel/DC they may ask for a scene-by-scene breakdown or other additional material to reassure them that you have it well planned out.
When you work with the same editor on multiple projects, that hyper-formalised process tends to lessen. A lot of my story pitches with editors who know me well are done via a few back-and-forth emails now instead of a highly structured document. Some story pitches are done over the phone. My editor knows I’m professional and can dance through formal hoops if necessary, so we cut it short and just get to work.
