Just clarifying - do you already have 2 bodies that you want to separate to individual models or do you have a single model that you want to split into 2? If you are trying to split 1 model into 2, try using a split line as the break edge. If you already have 2 bodies, you can choose to save a body as a separate part.
The above will work for parts or multibody parts. If you are actually in an assembly, you will have to split from within the individual part.
If by "bodies" you are referring to parts, you can create subassemblies from the parent assembly.