I mean as far as I know no human being is even a billionaire anyway if you only count cash. It's one of the things the "eat the rich" crowd is particularly bad at internalizing, that there's a difference between value and money that can be spent on food or hospitals.
2,000 gold bars were stopped out of iraq. and that is just what was stopped / reported.
Dictators and autocrats may or nay not have cash sitting in a bank account, but there are most likely multiple with $1B in gold.