If I got an interdisciplinary degree with 18 credit hours in each of two areas, would that get me into a doctoral program in either of those two areas, or would the doctorate have to be in interdisciplinary studies, or liberal arts, humanities, etc.?
It would vary by doctoral program, of course, but in general I'd guess it would qualify you for admission, but that you might have to take a few Master's level courses in that area if they think you're a little deficient. -=Steve=-