Detroit, MI to American University buses and trains from $74

Or, see buses and trains from American University to Detroit, MI.
Here are some trips other travelers have found on Routefriend.
15h 4m
2 stops
Amtrak Megabus
15h 25m
1 stop
16h 30m
2 stops
Greyhound Megabus
17h 15m
2 stops
Greyhound Amtrak