It sounds like you are proposing to skip the first segment of your trip. This is an extremly high risk manuever, as NW computers will catch this immediately and cancel out the rest of your iternary. You will then be at the mercy of someone at DTW to let you fly...
Let me give you an example, I was flying an award ticket IND-DTW-FNT (12 hour advance purchase don't shoot me!). For some reason my boarding pass was not scanned in DTW for my RJ segment down to FNT. Within a couple hours I noticed that my entire reservation had disappeared from NWA.com and I had to go back down to FNT's ticket counter to get the ticket reinstated.
Just a cautionary tale...