Permanently remove a device from your account page

What to do before you sell, give away or trade in your iPhone, iPad or iPod touch – Apple Support

these steps should dissociate the two

the blue text I write is a link to a page which describe how to remove an ios device from an appleID account,

the permanent is given that the user of the appleID does not setup the ios device to the appleID once again, the owner of the said appleID can only do this with the ios device in his and or her procession.