13
I downloaded the JavaFx source code from http://hg.openjdk.java.net/openjfx/2.2/master/rt/summary.
The name of the folder in the zip file is re-e71070b0e0c0.
I unzipped this and added the folder under Project Structure - Global Libraries in Idea, however it doesn't work. When I try to open a class it just shows field names and /* compiled code */. I couldn't find anything in the manual.