First off, I assume you mean Delta and not Northwest as the Delta/Northwest merger is totally completed and Northwest is officially no longer in existence. $247 is not a terrible price and fares are up a bit than they were last year. I flew NWA/Delta last December, but it was in the beginning of December, and I paid $150 round trip - that included fees/taxes. I'm sure it is more to fly to Florida the closer it gets to Christmas.
I just flew to DTW to MCO over Easter and I paid $349 round trip and that was actually a really good price for that time of year. A few weeks before the trip, one of my sons wanted to come with us and the fare was anywhere from $800 to $1,200 on any given day. No way was he going to pay that, so he is going in May and asked me to come with him to keep him company. I just booked air fare last week for that May trip and I think it was $202 round trip. I had talked to my son while I was at WDW because I wanted to make a bounceback reservation and he checked air fares for me and it was only $150, but he never booked. He waited for me to get home and by then it went up to $202. I watched it for a few days and it even went higher a couple of times so when it went down to the $202, I figured that was close enough for me and I haven't checked it since then because I don't want to know if it ever went back down to the $150.
The only other airline I have flown out of DTW to MCO was Southwest, but since they don't have any non stop flights out of Detroit anymore, I just go with Delta. They have to many non-stop flights to choose from and I have never had any problems at all with Delta or Northwest for that matter.