diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index 7fd7accc6b..8bd51dc71f 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -359,6 +359,8 @@ def column_for_attribute(name)
# "2004-12-12" in a date column is cast to a date object, like Date.new(2004, 12, 12)). It raises
# ActiveModel::MissingAttributeError if the identified attribute is missing.
#
+ # Note: +:id+ is always present.
+ #
# Alias for the read_attribute method.
#
# class Person < ActiveRecord::Base