ido-mode

ido-mode is a variable defined in `ido.el'.
Its value is

nil

Documentation:
Determines for which buffer/file Ido should be enabled.
The following values are possible:
- `buffer': Turn only on Ido buffer behavior (switching, killing,
displaying...)
- `file': Turn only on Ido file behavior (finding, writing, inserting...)
- `both': Turn on Ido buffer and file behavior.
- nil: Turn off any Ido switching.

Setting this variable directly does not take effect;
use either M-x customize or the function `ido-mode'.

You can customize this variable.