The Patriots won that pick ’em, but the underdog actually won the previous three Super Bowls outright — Seahawks (2014), Ravens (2013) and Giants (2012).
Super Bowl XIII between the Steelers and Cowboys is often referred to as "Black Sunday" for the Vegas sportsbooks. Pittsburgh opened as a 3½-point favorite, moved up to 4.5 before settling at 4. The Steelers won 35-31, meaning people who bet on the Cowboys late (taking the points at 4½) won, while people who bet on the Steelers early (at 3½) also won.
The largest Super Bowl favorite won and covered when the 49ers crushed the Chargers 49-26 as 18½-point favorites in XXIX.
The second largest Super Bowl favorite lost outright — Joe Namath and the Jets were 18-point underdogs when they shocked the Baltimore Colts 16-7 in III.
As for the over/under, the over has a slight 25-23 advantage — there was no over/under line for Super Bowl I — with the over hitting in four of the last five matchups.
Looking at the history of Super Bowl 50’s participants:
Denver is 2-5 straight up, 2-5 against the spread, 1-2 as a favorite (losing in XXII and XLVIII), and 1-3 as a dog, winning outright in XXXII.
Peyton Manning is 1-2 in his three appearances. His team was favored all three times as he won with the Colts in XLI, lost with the Colts in XLIV and lost with the Broncos in XLVIII.
Carolina covered in its only Super Bowl appearance, but lost to the Patriots 32-29 as a seven-point dog in XXXVIII.
Below is a history of every Super Bowl and every line (courtesy of Vegasinsider.com).