FNT and DTW are considered co-terminals, and a year or so ago I had a flight that was supposed to originate from FNT, but NW let me depart from DTW. I was flying FNT-DTW-ATL-SFO. The DTW-ATL leg on DL was cancelled, and NW put me on DTW-SFO nonstop. Not sure if it was because of the change or co-terminal, but I ended up leaving from DTW, not FNT. Nothing like cancellation happened to my ticket.