If you are using Intellij 14, and want to enable the return type of a method call in Scala (when the mouse stays for more than xxx millisecond).

You need to open your preferences, and Open “Languages and Frameworks” in the hierarchy (menu on the left), and select Scala Compile Server.

Ensure that the _**Show type info on mouse motion with delay**_ option is ticked.

This will enable this feature.

Screen Shot 2014-12-14 at 20.28.00