Emacs 実践入門の anything-for-document が便利だったので helm 用に作りなおした！

helm-for-document.el

;; helm-for-document
(require 'helm-elisp)
(setq helm-for-document-sources-info
             (list
               helm-c-source-info-emacs
               helm-c-source-info-elisp
               helm-c-source-info-gnus
               helm-c-source-info-pages
               helm-c-source-info-org
               helm-c-source-info-cl))
(setq helm-for-document-sources
      (nconc
      (mapcar (lambda (func)
                (funcall func))
              '(helm-c-source-emacs-commands
                helm-c-source-emacs-functions
                helm-c-source-emacs-variables
                helm-c-source-emacs-faces
                helm-c-source-helm-attributes))
      helm-for-document-sources-info))

(defun helm-for-document ()
  "Preconfigured `helm' for helm-for-document."
  (interactive)
  (helm
   :sources helm-for-document-sources
   :input (thing-at-point 'symbol)
   :resume nil
   :preselect nil
   :buffer "*helm for document*"
   :candidate-number-limit 20))
(define-key global-map (kbd "M-s-d") 'helm-for-document)