diff --git a/core/lib/Drupal/Core/Entity/EntityTypeBundleInfo.php b/core/lib/Drupal/Core/Entity/EntityTypeBundleInfo.php
index 42d00a7..e454eee 100644
--- a/core/lib/Drupal/Core/Entity/EntityTypeBundleInfo.php
+++ b/core/lib/Drupal/Core/Entity/EntityTypeBundleInfo.php
@@ -19,7 +19,9 @@ class EntityTypeBundleInfo implements EntityTypeBundleInfoInterface {
   /**
    * Static cache of bundle information.
    *
-   * @var array
+   * @var array[]
+   *   The array has the same structure as the return value of
+   *   \Drupal\Core\Entity\EntityTypeBundleInfoInterface::getAllBundleInfo().
    */
   protected $bundleInfo;
 
diff --git a/core/lib/Drupal/Core/Entity/EntityTypeBundleInfoInterface.php b/core/lib/Drupal/Core/Entity/EntityTypeBundleInfoInterface.php
index 4425d28..dd9b78b 100644
--- a/core/lib/Drupal/Core/Entity/EntityTypeBundleInfoInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityTypeBundleInfoInterface.php
@@ -10,8 +10,12 @@
   /**
    * Get the bundle info of all entity types.
    *
-   * @return array
-   *   An array of all bundle information.
+   * @return array[]
+   *   An array of all bundle information, of which keys are entity type IDs and
+   *   values are arrays of which keys are bundle names, and values are arrays
+   *   with the same structure as the return value of static::getBundleInfo().
+   *
+   * @see static::getBundleInfo()
    */
   public function getAllBundleInfo();
 
@@ -19,10 +23,18 @@ public function getAllBundleInfo();
    * Gets the bundle info of an entity type.
    *
    * @param string $entity_type
-   *   The entity type.
+   *   The entity type ID.
    *
-   * @return array
-   *   Returns the bundle information for the specified entity type.
+   * @return mixed[]
+   *   An array of bundle information of which keys are bundle names and values
+   *   are arrays with the following keys:
+   *   - label: The human-readable name of the bundle.
+   *   - uri_callback: The same as the 'uri_callback' key defined for the entity
+   *     type in its definition, but for the bundle only. When determining the
+   *     URI of an entity, if a 'uri_callback' is defined for both the entity
+   *     type and the bundle, the one for the bundle is used.
+   *   - translatable: (optional) TRUE if the bundle has translation support,
+   *     FALSE (default) if not.
    */
   public function getBundleInfo($entity_type);
 
diff --git a/core/lib/Drupal/Core/Entity/entity.api.php b/core/lib/Drupal/Core/Entity/entity.api.php
index ca8bef5..3fb3d16 100644
--- a/core/lib/Drupal/Core/Entity/entity.api.php
+++ b/core/lib/Drupal/Core/Entity/entity.api.php
@@ -706,16 +706,10 @@ function hook_entity_view_mode_info_alter(&$view_modes) {
 /**
  * Describe the bundles for entity types.
  *
- * @return array
- *   An associative array of all entity bundles, keyed by the entity
- *   type name, and then the bundle name, with the following keys:
- *   - label: The human-readable name of the bundle.
- *   - uri_callback: The same as the 'uri_callback' key defined for the entity
- *     type in the EntityManager, but for the bundle only. When determining
- *     the URI of an entity, if a 'uri_callback' is defined for both the
- *     entity type and the bundle, the one for the bundle is used.
- *   - translatable: (optional) A boolean value specifying whether this bundle
- *     has translation support enabled. Defaults to FALSE.
+ * @return array[]
+ *   An array of all bundle information with the same structure as the return
+ *   value of
+ *   \Drupal\Core\Entity\EntityTypeBundleInfoInterface::getAllBundleInfo().
  *
  * @see entity_get_bundles()
  * @see hook_entity_bundle_info_alter()
@@ -728,8 +722,10 @@ function hook_entity_bundle_info() {
 /**
  * Alter the bundles for entity types.
  *
- * @param array $bundles
- *   An array of bundles, keyed first by entity type, then by bundle name.
+ * @param array[] $bundles
+ *   An array of all bundle information with the same structure as the return
+ *   value of
+ *   \Drupal\Core\Entity\EntityTypeBundleInfoInterface::getAllBundleInfo().
  *
  * @see entity_get_bundles()
  * @see hook_entity_bundle_info()