The Fortune 500 financial services company erroneously credited $81 trillion, instead of just $280, to a customer’s account last April, the Financial Times reported on Friday. The error got past two employees before a third caught it 90 minutes after it had been posted, according to internal documents seen by the FT and two people familiar with the matter. 

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, our detective controls promptly identified the inputting error between two Citi ledger accounts, and we reversed the entry,” a Citigroup spokesperson told Fortune in a statement. “Our preventative controls would have also stopped any funds leaving the bank.”

Still, it took several hours to reverse the transaction, according to the FT, unveiling operational weaknesses at the bank. 

The Citigroup spokesperson said there was “no impact to the bank or our client,” but the episode underscores the bank’s efforts to eliminate manual processes.

“If a bank can misplace $81 trillion, what does that say about its ability to safeguard the average consumer’s paycheck? Citi’s latest blunder isn’t just a glitch—it’s a flashing warning sign that operational risk is still a ticking time bomb in banking,” Anna Kooi, national financial services and institutions practice leader at accounting and advisory firm Wipfli, told Fortune. 

Citigroup had a total of 10 near misses of at least $1 billion last year, down from 13 the previous year, an internal report reviewed by the FT shows. A near miss occurs when a bank processes the wrong amount but ends up being able to recover the transaction funds. 

“If two employees processed the transaction without catching the mistake, it indicates potential gaps in training, alert thresholds, or even cultural complacency around due diligence,” Kooi said.

This episode also marks a major setback for Citigroup, which has been under regulatory scrutiny for years over its risk management and operations practices. Bank regulators have demanded improvements, and this $81 trillion mistake could show Citigroup hasn’t addressed its operational weaknesses, she added.

One such example was when, in 2020, Citigroup accidentally wired $900 million to a group of lenders at beauty company Revlon instead of an intended interest payment of just $7.8 million. That event led to a two-year legal battle and a $400 million fine from the Office of the Comptroller of the Currency. In 2024, the bank was also fined $136 million for failing to fix data management issues. 

In January, Citigroup chief financial officer Mark Mason said the bank was making an effort to address compliance issues. 

“We saw the need to invest more in the transformation on data, on technology, on improving the quality of the information coming out of our regulatory reporting,” Mason told reporters.

Citigroup had several near misses last year, but “errors of this magnitude are incredibly rare, especially given the millions of transactions major banks process daily,” Andrew Latham, a certified financial planner, told Fortune. “But they serve as reminders that even well-established systems aren’t infallible.”