To detach the tty without exiting the shell, use the escape sequence Ctrl+P followed by Ctrl+Q. More details here.
Additional info from this source:
docker run -t -i → can be detached with ^P^Qand reattached with docker attach
docker run -i → cannot be detached with ^P^Q; will disrupt stdin
docker run → cannot be detached with ^P^Q; can SIGKILL client; can reattach with docker attach