You aren't going to be able to get from SFO-DTW on all widebodies.
NW isn't operating and widebodies at all to either DTW or MSP anymore, so its not possible even with a connection. NW is running a 757 between SFO-DTW, I'd take that one over the A320's.
AA is running a few 767 flights between SFO-ORD, but then you'd have to connect onto something smaller either an MD-80 or F-100 for the short hop from ORD-DTW. Its a real short flight so that may not be too bad.
UA runs a ton of widebodies from SFO-ORD. A 747-400 a ton of 777's, a couple 767's. They run mostly 737's and A320's ORD-DTW, a maybe a 757.
You're best be to be on mostly widebodies is United. You can definetely get a 747 or 777 from SFO-ORD, which is the bulk of the flying time. You'll have to take a narrowbody on the short hop over to DTW.