diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigStorageController.php b/core/lib/Drupal/Core/Config/Entity/ConfigStorageController.php
index 730aaa2..6799b1f 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigStorageController.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigStorageController.php
@@ -131,7 +131,7 @@ public function loadMultiple(array $ids = NULL) {
       // Remove any invalid ids from the array.
       $passed_ids = array_intersect_key($passed_ids, $entities);
       foreach ($entities as $entity) {
-        $passed_ids[$entity->{$this->idKey}] = $entity;
+        $passed_ids[$entity->id()] = $entity;
       }
       $entities = $passed_ids;
     }
@@ -310,11 +310,6 @@ public function save(EntityInterface $entity) {
       $entity->original = $this->loadUnchanged($id);
     }
 
-    // Build an ID if none is set.
-    if (!isset($entity->{$this->idKey})) {
-      $entity->{$this->idKey} = $entity->id();
-    }
-
     $entity->preSave($this);
     $this->invokeHook('presave', $entity);
 
diff --git a/core/modules/entity/lib/Drupal/entity/EntityDisplayBase.php b/core/modules/entity/lib/Drupal/entity/EntityDisplayBase.php
index 1a2bc5e..b33b3d9 100644
--- a/core/modules/entity/lib/Drupal/entity/EntityDisplayBase.php
+++ b/core/modules/entity/lib/Drupal/entity/EntityDisplayBase.php
@@ -23,7 +23,7 @@
    *
    * @var string
    */
-  public $id;
+  protected $id;
 
   /**
    * Entity type to be displayed.
@@ -198,7 +198,6 @@ public function postSave(EntityStorageControllerInterface $storage_controller, $
    */
   public function toArray() {
     $names = array(
-      'id',
       'uuid',
       'targetEntityType',
       'bundle',
@@ -208,7 +207,9 @@ public function toArray() {
       'status',
       'dependencies'
     );
-    $properties = array();
+    $properties = array(
+      'id' => $this->id(),
+    );
     foreach ($names as $name) {
       $properties[$name] = $this->get($name);
     }
diff --git a/core/modules/entity/lib/Drupal/entity/Tests/EntityDisplayTest.php b/core/modules/entity/lib/Drupal/entity/Tests/EntityDisplayTest.php
index 31ea4e8..d6ab365 100644
--- a/core/modules/entity/lib/Drupal/entity/Tests/EntityDisplayTest.php
+++ b/core/modules/entity/lib/Drupal/entity/Tests/EntityDisplayTest.php
@@ -104,7 +104,7 @@ public function testEntityGetDisplay() {
     // Check that entity_get_display() returns the correct object.
     $display = entity_get_display('entity_test', 'entity_test', 'default');
     $this->assertFalse($display->isNew());
-    $this->assertEqual($display->id, 'entity_test.entity_test.default');
+    $this->assertEqual($display->id(), 'entity_test.entity_test.default');
     $this->assertEqual($display->getComponent('component_1'), array('weight' => 10));
   }
 
diff --git a/core/modules/entity/lib/Drupal/entity/Tests/EntityFormDisplayTest.php b/core/modules/entity/lib/Drupal/entity/Tests/EntityFormDisplayTest.php
index eb0477f..428222b 100644
--- a/core/modules/entity/lib/Drupal/entity/Tests/EntityFormDisplayTest.php
+++ b/core/modules/entity/lib/Drupal/entity/Tests/EntityFormDisplayTest.php
@@ -45,7 +45,7 @@ public function testEntityGetFromDisplay() {
     // Check that entity_get_form_display() returns the correct object.
     $form_display = entity_get_form_display('entity_test', 'entity_test', 'default');
     $this->assertFalse($form_display->isNew());
-    $this->assertEqual($form_display->id, 'entity_test.entity_test.default');
+    $this->assertEqual($form_display->id(), 'entity_test.entity_test.default');
     $this->assertEqual($form_display->getComponent('component_1'), array('weight' => 10));
   }
 
diff --git a/core/modules/field/lib/Drupal/field/Entity/FieldConfig.php b/core/modules/field/lib/Drupal/field/Entity/FieldConfig.php
index 20ff0de..edb737a 100644
--- a/core/modules/field/lib/Drupal/field/Entity/FieldConfig.php
+++ b/core/modules/field/lib/Drupal/field/Entity/FieldConfig.php
@@ -239,7 +239,6 @@ public function id() {
    */
   public function toArray() {
     $names = array(
-      'id',
       'uuid',
       'status',
       'langcode',
@@ -254,7 +253,9 @@ public function toArray() {
       'indexes',
       'dependencies',
     );
-    $properties = array();
+    $properties = array(
+      'id' => $this->id(),
+    );
     foreach ($names as $name) {
       $properties[$name] = $this->get($name);
     }
diff --git a/core/modules/field/lib/Drupal/field/Entity/FieldInstanceConfig.php b/core/modules/field/lib/Drupal/field/Entity/FieldInstanceConfig.php
index 2b8e87f..35b3775 100644
--- a/core/modules/field/lib/Drupal/field/Entity/FieldInstanceConfig.php
+++ b/core/modules/field/lib/Drupal/field/Entity/FieldInstanceConfig.php
@@ -283,7 +283,7 @@ public function __construct(array $values, $entity_type = 'field_instance_config
    * {@inheritdoc}
    */
   public function id() {
-    return $this->entity_type . '.' . $this->bundle . '.' . $this->field->name;
+    return $this->entity_type . '.' . $this->bundle . '.' . $this->field_name;
   }
 
   /**
@@ -291,7 +291,6 @@ public function id() {
    */
   public function toArray() {
     $names = array(
-      'id',
       'uuid',
       'status',
       'langcode',
@@ -307,7 +306,9 @@ public function toArray() {
       'settings',
       'dependencies',
     );
-    $properties = array();
+    $properties = array(
+      'id' => $this->id(),
+    );
     foreach ($names as $name) {
       $properties[$name] = $this->get($name);
     }
diff --git a/core/modules/rdf/lib/Drupal/rdf/Entity/RdfMapping.php b/core/modules/rdf/lib/Drupal/rdf/Entity/RdfMapping.php
index 4c5284f..41a5f91 100644
--- a/core/modules/rdf/lib/Drupal/rdf/Entity/RdfMapping.php
+++ b/core/modules/rdf/lib/Drupal/rdf/Entity/RdfMapping.php
@@ -138,14 +138,15 @@ public function id() {
    */
   public function toArray() {
     $names = array(
-      'id',
       'uuid',
       'targetEntityType',
       'bundle',
       'types',
       'fieldMappings',
     );
-    $properties = array();
+    $properties = array(
+      'id' => $this->id(),
+    );
     foreach ($names as $name) {
       $properties[$name] = $this->get($name);
     }