In the information on Baggage Value on delta.com is the following statement (the bolding is mine):
Delta is not responsible or liable for cash, camera equipment, commercial effects, computer software and equipment, electronic equipment, fragile articles, jewelry, lifesaving medication, negotiable papers, irreplaceable business documents, works of art or other similar valuable items contained in checked or unchecked baggage. These types of items should be carried on — and kept in sight.