Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/book/config/install/field.field.node.book.body.yml

@@ -0,0 +1,22 @@
+langcode: en
+status: true
+dependencies:
+  config:
+    - field.storage.node.body
+    - node.type.book
+  module:
+    - text
+id: node.book.body
+field_name: body
+entity_type: node
+bundle: book
+label: Body
+description: ''
+required: false
+translatable: true
+default_value: {  }
+default_value_callback: ''
+settings:
+  display_summary: true
+third_party_settings: {  }
+field_type: text_with_summary