diff --git a/core/includes/form.inc b/core/includes/form.inc
index 15ef023..9865e2f 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -241,7 +241,7 @@ function template_preprocess_fieldset(&$variables) {
 function template_preprocess_details(&$variables) {
   $element = $variables['element'];
   Element::setAttributes($element, ['id']);
-  Element\RenderElement::setAttributes($element);
+  RenderElement::setAttributes($element);
   $variables['attributes'] = $element['#attributes'];
   $variables['summary_attributes'] = new Attribute();
   if (!empty($element['#title'])) {
diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
index 2c36a22..c4a1fd2 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -901,12 +901,11 @@ public function doBuildForm($form_id, &$element, FormStateInterface &$form_state
       $element['#defaults_loaded'] = TRUE;
     }
     // Assign basic defaults common for all form elements.
-    // Note that #description_display is below by default, except for details.
     $element += [
       '#required' => FALSE,
       '#attributes' => [],
       '#title_display' => 'before',
-      '#description_display' => (isset($element['#type']) && $element['#type'] == 'details') ? 'before' : 'after',
+      '#description_display' => 'after',
       '#errors' => NULL,
     ];
 
diff --git a/core/lib/Drupal/Core/Render/Element/Details.php b/core/lib/Drupal/Core/Render/Element/Details.php
index 92bbb32..fb3e74c 100644
--- a/core/lib/Drupal/Core/Render/Element/Details.php
+++ b/core/lib/Drupal/Core/Render/Element/Details.php
@@ -44,6 +44,7 @@ public function getInfo() {
     return [
       '#open' => FALSE,
       '#value' => NULL,
+      '#description_display' => 'before',
       '#process' => [
         [$class, 'processGroup'],
         [$class, 'processAjaxForm'],
diff --git a/core/modules/system/src/Tests/Form/ElementsLabelsTest.php b/core/modules/system/src/Tests/Form/ElementsLabelsTest.php
index 01254a8..549e8e4 100644
--- a/core/modules/system/src/Tests/Form/ElementsLabelsTest.php
+++ b/core/modules/system/src/Tests/Form/ElementsLabelsTest.php
@@ -107,19 +107,19 @@ public function testFormDescriptions() {
     $field_id = 'edit-form-textfield-test-description-default';
     $description_id = $field_id . '--description';
     $elements = $this->xpath('//input[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]/following-sibling::div[@id="' . $description_id . '"]');
-    $this->assertTrue(isset($elements[0]), 'Properly places by default the #description element after the form item.');
+    $this->assertTrue(isset($elements[0]), t('Properly places by default the #description element after the form item.'));
 
     // Check #description placement with #description_display='after'.
     $field_id = 'edit-form-textfield-test-description-after';
     $description_id = $field_id . '--description';
     $elements = $this->xpath('//input[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]/following-sibling::div[@id="' . $description_id . '"]');
-    $this->assertTrue(isset($elements[0]), 'Properly places the #description element after the form item.');
+    $this->assertTrue(isset($elements[0]), t('Properly places the #description element after the form item.'));
 
     // Check #description placement with #description_display='before'.
     $field_id = 'edit-form-textfield-test-description-before';
     $description_id = $field_id . '--description';
     $elements = $this->xpath('//input[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]/preceding-sibling::div[@id="' . $description_id . '"]');
-    $this->assertTrue(isset($elements[0]), 'Properly places the #description element before the form item.');
+    $this->assertTrue(isset($elements[0]), t('Properly places the #description element before the form item.'));
 
     // Check if the class is 'visually-hidden' on the form element description
     // for the option with #description_display='invisible' and also check that
@@ -127,7 +127,38 @@ public function testFormDescriptions() {
     $field_id = 'edit-form-textfield-test-description-invisible';
     $description_id = $field_id . '--description';
     $elements = $this->xpath('//input[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]/following-sibling::div[contains(@class, "visually-hidden")]');
-    $this->assertTrue(isset($elements[0]), 'Properly renders the #description element visually-hidden.');
+    $this->assertTrue(isset($elements[0]), t('Properly renders the #description element visually-hidden.'));
+
+
+    $this->drupalGet('form-test/group-details');
+
+    // Check #description default placement in a 'details' element.
+    $field_id = 'edit-meta';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div/preceding-sibling::div');
+    $this->assertTrue(isset($elements[0]), 'Properly places by default the #description element before the form item within details group.');
+
+    // Check #description placement with #description_display='before' in a
+    // 'details' element.
+    $field_id = 'edit-details-before';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div[@id="edit-meta-before"]/preceding-sibling::div[@id="' . $description_id . '"]');
+    $this->assertTrue(isset($elements[0]), 'Properly places the #description element before the form item within details group.');
+
+    // Check #description placement with #description_display='after' in a
+    // 'details' element.
+    $field_id = 'edit-details-after';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div[@id="edit-meta-after"]/following-sibling::div[@id="' . $description_id . '"]');
+    $this->assertTrue(isset($elements[0]), 'Properly places the #description element after the form item within details group.');
+
+    // Check if the class is 'visually-hidden' on the form details description
+    // for the option with #description_display='invisible' and also check that
+    // the description is placed after the form element.
+    $field_id = 'edit-details-invisible';
+    $description_id = $field_id . '--description';
+    $elements = $this->xpath('//details[@id="' . $field_id . '" and @aria-describedby="' . $description_id . '"]//div[@id="edit-meta-invisible"]/following-sibling::div[contains(@class, "visually-hidden")]');
+    $this->assertTrue(isset($elements[0]), 'Properly renders the #description element visually-hidden within details group.');
   }
 
   /**
diff --git a/core/themes/stable/templates/form/details.html.twig b/core/themes/stable/templates/form/details.html.twig
index 0484677..ccd2796 100644
--- a/core/themes/stable/templates/form/details.html.twig
+++ b/core/themes/stable/templates/form/details.html.twig
@@ -31,7 +31,7 @@
     </div>
   {% endif %}
 
-  {{ description.content }}
+  {{ description }}
   {{ children }}
   {{ value }}
 </details>