USD are ultimately bearer notes, we've just built a bunch of trust-based infrastructure to enable transactions without moving physical currency. The key featur

USD are ultimately bearer notes, we've just built a bunch of trust-based infrastructure to enable transactions without moving physical currency. The key feature of this system (and what everyone is ignoring) is bank accounts that x/German bank has at y/Russia bank (this is also the actual means of transaction for SWIFT). So in your example, 'y bank erroneously says we have $100tn' would actually just mean 'y bank is willing to credit the account of x bank by $100tn.' If x bank then tried to pay y bank for a separate transaction with those fake $, then y bank is the loser anyway. EDIT: Put alternatively, 'making up' USD is a near equivalent to making a loan, which is sort of the core thing a bank does anyway.