Can you fly out the 17th instead of the 18th? If so, you might be able to book a United R/T award with a stopover in FRA. Looks like the 17th is the last day with award seats prior to Christmas.
So the award would be DTW-FRA(stop)-LED-DTW. Between 60k and 100k depending on how much Y vs. J you want. (The cleanest routes seemed to have Y going over and J coming back.)
FRA-MAN-FRA would be about $250 for LH nonstops.
That avoids a big NYC transit/hotel hassle as well as a London transit/train hassle. Bonus for avoiding both the NYC area and Chicago, two places I wouldn't want to unnecessarily inject into a winter trip. (I mean, I know you gotta start in Detroit, but no need to make this worse than necessary, right?

)
All of that said, it might be tempting to just buy DTW-MAN (or LON) -LED-DTW via the most direct routings possible. Any decent winter fares loaded yet? Seems like you're flying far enough ahead of Christmas to get decent fares.