Plenty of time. All you will have to do is go through a transit security checkpoint, no Immigration or Customs. Your bags should be tagged all the way through to BKK when you check in at DTW, they'll be routed to BKK automatically so no need to deal with personally at NRT. FWIW, DL (well, old NW) used to have connections as short as 45 min scheduled at NRT! NRT is very efficient and if your incoming flight is late and makes the connection to BKK tight, usually uniformed airport staff will be holding up signs by the security checkpoint, looking for transit passengers that need to make their connections quickly, and get you to the front of the lines. NRT is very efficient and staff are professional and polite.