You'd have zero gambling losses for the year, under this scenario, since you actually had no losses.
All you would report are the $20,000 in gambling winnings.
If you then made a $20,000 bet, for example, and you lost it, you could deduct that $20,000. If you'd bet $25,000 instead of $20,000 and lost it, you'd only be able to claim $20,000, since that was the extent of your winnings for the year.
