ido-max-directory-size

ido-max-directory-size is a variable defined in `ido.el'.
Its value is

nil

Documentation:
Maximum size (in bytes) for directories to use Ido completion.

Uses keymap `ido-completion-map', which is not currently defined.

If you enter a directory with a size larger than this size, Ido will
not provide the normal completion. To show the completions, use M-x ido-toggle-ignore.

You can customize this variable.