Winters are shorter, but the temperatures drop
much lower than in Denmark, anyway (perhaps not colder than Finland). Here are the nightly low temperatures in Chicago for the next 5 days: -17 C, -20 C, -25 C, -22 C, -13 C. I have never seen temperatures like that in Copenhagen!
Granted, in an average week Chicago won't be quite that cold, but in general its winter weather is pretty harsh. People bike to work all winter in Copenhagen, which would be unthinkable in Chicago weather (even if the city had better bike infrastructure). I actually like it being moderately cold and snowy, but -5 C is about my limit.