Orphan records

The Orphan Records Control section of a relationship allows you to specify whether or not related records get deleted when the parent record is deleted. For example, if a user deletes a quote record, it might make sense to delete all of the related line item records. But the opposite case is not true; if a user deletes a line item, it does not make sense to delete the related quote record. Edit the relationship component in the object definition to change this behavior.

From the above screen shot, detach links for Line-Item are not available in places such as related list view. This is expected as it prevents the possibility of any line items turn into orphan records.