The rest of the money exists electronically. This is because most countries use what is called Fiat Money, which means that the currency is just a representation of value.
Here's a good way to understand why so much of the money today is electronic: if I send you $20 on a bank wire with no physical bill associated vs. giving you a $20 bill, or giving you $20 worth of gold. What is the difference between wiring $20 and giving you a $20 bill? Nothing really, it's just a different way of transmitting information about money, and placing that amount from one person to another. There is nothing inherently valuable about the paper that the $20 is printed on. On the other hand, gold is considered to have inherent value by itself. Me giving you $20 worth of gold is an actual transfer of a valuable good. Once countries decided not to trade money in gold or precious metals, the need for physical bills diminished, and in the future, money will only become more and more digital.
Here are some other fun facts about money:
- The first credit card was issued in 1950 by Diners Club.
- After WWII, banks began putting all their transactions on magnetic reels and sending them to the Federal Reserve Bank, this eliminated the need for the $500, $1,000, $5,000, and $10,000 bills.
- Credit cards were initially just for rich businessmen, but quickly it became clear to banks that they could make millions if they offered them to everyone.
- Visa is the largest credit card company in the world. There are over 200 million Visa cards in use in the U.S. alone.