Hi I have figured out why I cannot see Documents and Data on my iPad. in order to use my iPad for work I have downloaded a Profile from work so I can connect to work's email. The security features of the Profile disable Documents and Data. So until I delete the Profile I cannot get access to Documents and Data (via iCloud sync) on my iPad.
I dont have this Profile on my iPhone as I have separate work phone. So that explains why I can see Documents and Data on my iPhone and not my iPad.
On your iPad go to Settings>General>Profile and see if there is a profile there which might be blocking you from seeing Documents and Data in your iCloud settings.