diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index 4fb39fde824a..8d75280a54d4 100644
--- a/docs/ref/models/fields.txt
+++ b/docs/ref/models/fields.txt
@@ -457,6 +457,9 @@ The primary key field is read-only. If you change the value of the primary
 key on an existing object and then save it, a new object will be created
 alongside the old one.
 
+The primary key field is set to ``None`` when
+:meth:`deleting <django.db.models.Model.delete>` an object.
+
 ``unique``
 ----------
 
diff --git a/docs/ref/models/instances.txt b/docs/ref/models/instances.txt
index c15427264b91..7e1c68b4d876 100644
--- a/docs/ref/models/instances.txt
+++ b/docs/ref/models/instances.txt
@@ -644,8 +644,9 @@ Deleting objects
 
 Issues an SQL ``DELETE`` for the object. This only deletes the object in the
 database; the Python instance will still exist and will still have data in
-its fields. This method returns the number of objects deleted and a dictionary
-with the number of deletions per object type.
+its fields, except for the primary key set to ``None``. This method returns the
+number of objects deleted and a dictionary with the number of deletions per
+object type.
 
 For more details, including how to delete objects in bulk, see
 :ref:`topics-db-queries-delete`.