Last I checked they only did syntax highlighting, not completion. And Jetbrains were rather clear that it was not a priority.

I am happy to be wrong now though.

Edit, this is a good step forward, here is the list from NetBeans, the "Toyota Hilux" of IDEs and my favorite:

    Language Feature Support Status
    File type recognition √
    Project type 
    Semantic syntax highlighting √
    Formatting √
    Braces matching √
    Code completion √
    Error Hints/Fixes/Suggestions 
    Code templates 
    Refactoring 
    Debugging

At the pace this is moving now I don't know what will stop me from only using Kotlin in the feature.