A lot - but not all - of it has been borrowed for worthwhile purposes.
Recently it's been leveling off:
This is the Parliamentary Library paper that explains what's been happening.
A commenter asked whether I thought the explosion in private foreign debt mattered much.
I replied that I didn't think it mattered much in and of itself.
But I noted that markets may (suddenly) take a (quite possibly irrational) set against it, which would make my own views beside the point.
I wrote about the danger here.