In a conference call with reporters, Dimon said the losses in a portfolio of credit investments occurred within the bank's Chief Investment Office, The New York Times reported.
"These were egregious mistakes," he said. "They were self-inflicted and this is not how we want to run a business."
The Chief Investment Office effects trades meant to balance assets and liabilities, and the losses will likely affect the company's overall earnings, the newspaper said.
The company said in a filing the Chief Investment Office is expected to report a second-quarter loss of $800 million. The final count will depend on what action the bank takes and how markets respond, but Dimon said it could "easily get worse."
"We have egg on our face," Dimon said. "We deserve any criticism we get."
Sen. Carl Levin, D-Mich., said after the disclosure the losses are an indication that financial reform is needed.
"The enormous loss JPMorgan announced today is just the latest evidence that what banks call 'hedges' are often risky bets that so-called 'too big to fail' banks have no business making," Levin, chairman of the Senate Permanent Subcommittee on Investigations, said in a statement issued by his office. "Today's announcement is a stark reminder of the need for regulators to establish tough, effective standards."