MSP can be tough because you're talking DL hub to DL hub. Getting to LGA isn't too bad considering there are flights every 30 minutes to an hour. But you'll occasionally see 20+ seats in the back the night before go negative the next morning. Of course the snowball effect only makes it worse. The real challenge is getting back to ATL from LGA. Seeing 100+ nonrevs on the list with an already oversold plane is not uncommon. Usually creative nonreving through like DCA is a possibility. Not too sure about DTW but I'd imagine it's like MSP. Hope that helps.