diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
index 4656897..0ab9a60 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.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/entity.module b/core/modules/entity/entity.module
index d01563b..e314b83 100644
--- a/core/modules/entity/entity.module
+++ b/core/modules/entity/entity.module
@@ -86,7 +86,7 @@ function entity_entity_bundle_rename($entity_type_id, $bundle_old, $bundle_new)
       $id = ConfigEntityStorage::getIDFromConfigName($id, $entity_type->getConfigPrefix());
       $display = entity_load('entity_view_display', $id);
       $new_id = $entity_type_id . '.' . $bundle_new . '.' . $display->mode;
-      $display->id = $new_id;
+      $display->set('id', $new_id);
       $display->bundle = $bundle_new;
       $display->save();
     }
@@ -100,7 +100,7 @@ function entity_entity_bundle_rename($entity_type_id, $bundle_old, $bundle_new)
       $id = ConfigEntityStorage::getIDFromConfigName($id, $entity_type->getConfigPrefix());
       $form_display = entity_load('entity_form_display', $id);
       $new_id = $entity_type_id . '.' . $bundle_new . '.' . $form_display->mode;
-      $form_display->id = $new_id;
+      $form_display->set('id', $new_id);
       $form_display->bundle = $bundle_new;
       $form_display->save();
     }
diff --git a/core/modules/entity/lib/Drupal/entity/EntityDisplayBase.php b/core/modules/entity/lib/Drupal/entity/EntityDisplayBase.php
index 79a8b01..dd1bfa0 100644
--- a/core/modules/entity/lib/Drupal/entity/EntityDisplayBase.php
+++ b/core/modules/entity/lib/Drupal/entity/EntityDisplayBase.php
@@ -198,7 +198,6 @@ public function postSave(EntityStorageInterface $storage, $update = TRUE) {
    */
   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/field/field.module b/core/modules/field/field.module
index 52f3996..db35e40 100644
--- a/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -200,7 +200,7 @@ function field_entity_bundle_rename($entity_type, $bundle_old, $bundle_new) {
   foreach ($instances as $instance) {
     if ($instance->entity_type == $entity_type && $instance->bundle == $bundle_old) {
       $id_new = $instance->entity_type . '.' . $bundle_new . '.' . $instance->field_name;
-      $instance->id = $id_new;
+      $instance->set('id', $id_new);
       $instance->bundle = $bundle_new;
       $instance->allowBundleRename();
       $instance->save();
diff --git a/core/modules/field/lib/Drupal/field/Entity/FieldConfig.php b/core/modules/field/lib/Drupal/field/Entity/FieldConfig.php
index ff54ff4..11c4f0d 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 aa77ef8..3eea9cb 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/field/lib/Drupal/field/FieldConfigStorage.php b/core/modules/field/lib/Drupal/field/FieldConfigStorage.php
index ba1803a..09fa119 100644
--- a/core/modules/field/lib/Drupal/field/FieldConfigStorage.php
+++ b/core/modules/field/lib/Drupal/field/FieldConfigStorage.php
@@ -135,7 +135,7 @@ public function loadByProperties(array $conditions = array()) {
 
       // When returning deleted fields, key the results by UUID since they can
       // include several fields with the same ID.
-      $key = $include_deleted ? $field->uuid : $field->id;
+      $key = $include_deleted ? $field->uuid() : $field->id();
       $matching_fields[$key] = $field;
     }
 
diff --git a/core/modules/image/lib/Drupal/image/Tests/ImageFieldDefaultImagesTest.php b/core/modules/image/lib/Drupal/image/Tests/ImageFieldDefaultImagesTest.php
index d162cd3..edf1919 100644
--- a/core/modules/image/lib/Drupal/image/Tests/ImageFieldDefaultImagesTest.php
+++ b/core/modules/image/lib/Drupal/image/Tests/ImageFieldDefaultImagesTest.php
@@ -115,7 +115,8 @@ public function testDefaultImages() {
       ->save();
 
     // Confirm the defaults are present on the article field settings form.
-    $this->drupalGet("admin/structure/types/manage/article/fields/$instance->id/field");
+    $instance_id = $instance->id();
+    $this->drupalGet("admin/structure/types/manage/article/fields/$instance_id/field");
     $this->assertFieldByXpath(
       '//input[@name="field[settings][default_image][fid][fids]"]',
       $default_images['field']->id(),
@@ -125,7 +126,7 @@ public function testDefaultImages() {
       )
     );
     // Confirm the defaults are present on the article field edit form.
-    $this->drupalGet("admin/structure/types/manage/article/fields/$instance->id");
+    $this->drupalGet("admin/structure/types/manage/article/fields/$instance_id");
     $this->assertFieldByXpath(
       '//input[@name="instance[settings][default_image][fid][fids]"]',
       $default_images['instance']->id(),
@@ -136,7 +137,7 @@ public function testDefaultImages() {
     );
 
     // Confirm the defaults are present on the page field settings form.
-    $this->drupalGet("admin/structure/types/manage/page/fields/$instance->id/field");
+    $this->drupalGet("admin/structure/types/manage/page/fields/$instance_id/field");
     $this->assertFieldByXpath(
       '//input[@name="field[settings][default_image][fid][fids]"]',
       $default_images['field']->id(),
@@ -146,7 +147,8 @@ public function testDefaultImages() {
       )
     );
     // Confirm the defaults are present on the page field edit form.
-    $this->drupalGet("admin/structure/types/manage/page/fields/$instance2->id");
+    $instance2_id = $instance2->id();
+    $this->drupalGet("admin/structure/types/manage/page/fields/$instance2_id");
     $this->assertFieldByXpath(
       '//input[@name="instance[settings][default_image][fid][fids]"]',
       $default_images['instance2']->id(),
@@ -185,7 +187,7 @@ public function testDefaultImages() {
     $field->save();
 
     // Confirm that the new default is used on the article field settings form.
-    $this->drupalGet("admin/structure/types/manage/article/fields/$instance->id/field");
+    $this->drupalGet("admin/structure/types/manage/article/fields/$instance_id/field");
     $this->assertFieldByXpath(
       '//input[@name="field[settings][default_image][fid][fids]"]',
       $default_images['field_new']->id(),
@@ -221,7 +223,7 @@ public function testDefaultImages() {
 
     // Confirm the new field instance default is used on the article field
     // admin form.
-    $this->drupalGet("admin/structure/types/manage/article/fields/$instance->id");
+    $this->drupalGet("admin/structure/types/manage/article/fields/$instance_id");
     $this->assertFieldByXpath(
       '//input[@name="instance[settings][default_image][fid][fids]"]',
       $default_images['instance_new']->id(),
@@ -259,7 +261,7 @@ public function testDefaultImages() {
     $instance->save();
 
     // Confirm the article field instance default has been removed.
-    $this->drupalGet("admin/structure/types/manage/article/fields/$instance->id");
+    $this->drupalGet("admin/structure/types/manage/article/fields/$instance_id");
     $this->assertFieldByXpath(
       '//input[@name="instance[settings][default_image][fid][fids]"]',
       '',
diff --git a/core/modules/rdf/lib/Drupal/rdf/Entity/RdfMapping.php b/core/modules/rdf/lib/Drupal/rdf/Entity/RdfMapping.php
index 985494c..e5783b7 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);
     }