Today I learned about the pydoc command from Python. Even if you're offline you can access the standard library documentation running from a local copy using the command mentioned above.
Simply introduce this command in your terminal:
$ pydoc -p 8000
Then you can go to http://locahost:8000. This way you can browse the documentation for all your installed Python modules in the same way you'd use the 'help' command from the Python CLI.