If you CTRL+O or CTRL+I, you are given an option to Copy the JavaDoc. It would be a nice bonus if the method walked up the tree for super methods or interface declarations if the target method did not have javadoc.
I discovered this while trying to override a method in Struts2. I had a class that extended ActionSupport. I hit CTRL+O to override getText(aTextName:String):String. I checked Copy JavaDoc, but nothing happened. It turns out that ActionSupport did not have any javadoc, but the method was the implementation of an interface method. The interface did have javadoc for the method. It would be great if IntelliJ used this javadoc since none was found initially.