If your IntelliJ is up to date, there is another solution.
I had the exact same problem in IntelliJ 2017.2 and it was driving me crazy until I read this post from a IntelliJ maintainer.
If you use IntelliJ Idea and "Load an existing project", it will model it as a Java project with a Python modules attached. You cannot get Django loaded, no matter what you do.
I handled this by purging the .idea directory, and created a new Django project, with the pre-existing Django directory as the base directory in IntelliJ. I can now see Django in the project structure > project settings > module part of Intellij, and I can select the django settings file.
Step by step in pictures
Delete .idea folder
Create new project 
Select Python > Django 
Hit next 
Select existing django project path (or start from scratch with a new folder) 
Add DJANGO_SETTINGS_MODULE=yourprojectname.settings to your run configuration (can be found in yourprojectname/wsgi.py file).


settings.pyfile which exists in your main project folder (this would have been automatically created for you), and the Manage Script should be set to the manage.py file which is in your project root.DJANGO_SETTINGS_MODULE=untitled.settingsto it. You'll want to separate them by a semicolon I believe...