Floating Nwell schematic and introduction in a MOS switch
The PFET will be implanted within an N-bulk region. If raw wafer is P-type, then a N-well must be added so the necessary PFETS can be built.

IN my experience, its your choice where to tie the N-wells. Dittos for PWell processes.

Handling high-voltage switching is a useful method, and those wells become your key to success. Of course there is lots of capacity from the well to bulk, and the displacement currents must be supplied, somehow.