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/field/lib/Drupal/field/Entity/FieldConfig.php b/core/modules/field/lib/Drupal/field/Entity/FieldConfig.php
index 2a7d5e5..3334a24 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 7da287c..1b81131 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/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 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);
     }