The Denver Broncos still have not been an underdog all season and it's unknown if that's going to change at this point. Earlier in the week, the lines dipped to have the Seattle Seahawks at +2.5 underdogs, at which time a lot of action came in on them to push it back down to +2. But the line has once again started trending in the other direction.
According to OddsShark, the current line has the Seahawks at +2.5, meaning the Broncos are -2.5. It's been right around there for much of the past week, and it sounds like the consistent money on Denver is not changing aside from the aforementioned spike.
The Broncos have been favored in 18 games this season, obviously counting the playoffs. They've fielded the most productive offense in NFL history; it just doesn't make sense to have them as the underdog. While the recent trends did show a spike toward Seattle that could drive the lines further, it seems unlikely to happen.
Bovada has the Broncos favored by three points, which is significant. Other sites sit at 2.5, while others still have a narrow -1 line for Denver, though that is a rarity at this point. At the time of writing, 62 percent of money is coming in on Denver, while 55 percent of the money is on the under for the total, which currently sits at 48.5.