It's simply picturesque (7)
I believe the answer is:
'picturesque' is the definition.
(I've seen this in another clue)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for idyllic that I've seen before include "Blissfully pastoral" , "Peaceful and happy, quite perfect" , "Heavenly" , "Delightful in every respect" , "Charming, picturesque" .)