Got a question for a very-tentative flight next summer.

I'll be flying home VS/EDI-LHR, DL/LHR-DTW. I know I'll need to change terminals and re-clear security, and I've got that time all planned out, but: will I need to gather my checked bag and re-check it, or will it be automatically transferred for me? I'm assuming it would be automatic, because DL and VS are joint venture (or whatever the right term is...), but I've never actually flown on a multiple-airline itinerary before, so I want to be sure.