FBI Director Robert Muller said the bureau has opened a preliminary investigation into a major JPMorgan Chase trading loss.

"All I can say is that we have opened a preliminary investigation," Robert Mueller said in response to questions at an FBI oversight hearing on Capitol Hill.

The company had made a surprise announce that it has suffered trading losses of $2 billion since the start of April.

The loss, while massive on the face of it, is expected to be easily absorbed by JPMorgan, which is the nation's largest bank by assets. Even this quarter, the bank is expected to turn a multi-billion dollar profit.

The group that suffered the losses is part of the bank's so-called corporate unit, and had been making trades designed to hedge against risk, which is a fancy way of saying it operates as a kind of insurance agency, CNNMoney.com reported. When a big bet is made, the office tries to find ways to mitigate the risk to the bank should the bet go south.

Over the past few months, the unit has staked out a very large position in insurance-like bets called credit default swaps, the same type of instrument that caused so much havoc in 2008.

CEO Jamie Dimon, who on Monday a $23 million compensation package approved, told analysts and reporters the losses were caused by "errors," "sloppiness" and "bad judgment."

In the wake of the financial crisis, critics have made the case that the biggest banks are still so large, so complex, and their desire for profits so great that they remain a systemic risk to the global financial system.

Dimon, in full damage control mode, was forced to hold a hastily-arranged conference call to announce the loss, and followed that with an appearance on Meet the Press, where he admitted the company had made a mistake.

"This is a terrible mistake," Dimon said. "In this job, you hope they're small and few and far between. This one is far too big."

Read more on JPMorgan:

CNNMoney.com: How JPMorgan made its $2B blunder

CNNMoney.com: Betting against JPMorgan

Fortune: The hedge funds that are profiting off JPMorgan's bad trade