well...if you're flying full fare, I think you can always fly HKG-SFO or HKG-LAX on CX first, and then connect to SFO/LAX-DTW on NW ? total timing shouldn't be that bad ?

(in fact, not necessarily full fare, but you can buy the 2 tickets separately ? but of course won't be as cheap as one NW ticket, and in case of delay etc the connection could be problematic)

if you want "fast" (i.e. no more than 1 connection?) - I don't think you have too many choices not using NW at all...or maybe via ORD on UA ?