It is important to note that SSDT is a little bit of an ambiguous term. SSDT is included on the SQL Server 2012/2014 media, but it is concerned with adding database project types. SSDT-BI is what BIDS once was and is now an external download. I personally think this leads to all kinds of confusion.

I think I read on the SQL Server 2016 data sheet that Microsoft is combining the SSDT/SSDT-BI products into the same component to help remove some of the confusion.