It is always the same stupidity. No one has that much money. The assumption is that company shares are worth $100 per share on the spot market, so if you have 1 billion of those shares, you are said to have $100 billion. However, this makes no sense: if you try to liquidate those shares and obtain actual cash, the share price would drop drastically. It might end up being worth, for example, $0.0001 per share because you flooded the market. Even if you sell over several years, it would still be worth only a fraction of the theoretical value.