Frank is a little unrealistic and idealistic (6)
I believe the answer is:
candid
'frank' is the definition.
(I know that frank can be written as candid)
'a little unrealistic and idealistic' is the wordplay.
'a little' indicates the answer is hidden within the clue (a little bit of the clue).
'CANDID' can be found hidden inside 'unrealistic and idealistic'.
'is' acts as a link.
(Other definitions for candid that I've seen before include "Very clear" , "Free and frank" , "Blunt; frank" , "Impartial" , "Frank - open" .)