
Citigroup accidentally credited a customer account $81 trillion instead of $280 last April. It took three employees and several hours to realize and correct the error.
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The event was considered a “near miss” because no funds actually left Citigroup. That amount would’ve been more than 1.5 times the market cap of the entire S&P 500—while dwarfing Citigroup’s own market cap of about $150 billion.
“Despite the fact that a payment of this size could not actually have been executed, ...
So what exactly would have happened if Citigroup had not caught and corrected the error? It's not like that $81 trillion actually existed.