"I'm not much of a gambler, but how much would have Floyd won if Michican did beat Bama by +14?"
Well Michigan only had to lose by less than 14 points. Maywether had Michigan +14 points.
The final score could have been; Alabama 30 Michigan 17, and Mayweather would have "covered" and won his bet.
He bet $3,000,000, so if Michigan had "covered" (won the game, or loss by less than 14 points) he would have won his $3,000,000 back plus another $3,000,000.
He may have had the bet at "-110" in which case all the above rules apply but his bet would have paid the original $3,000,000 back plus $2,900 000. The $100,000 is the casino "vig" or "take" for accepting the wager.