United States and British regulators have fined American finance company JP Morgan $US920 million in relation to losses made by a trader known as the "London whale".
The bank lost more than $6 billion in the trades at the beginning of last year.
In a statement, the US Securities and Exchange Commission described JP Morgan's accounting controls as "woefully deficient".
The British Financial Conduct Authority said the bank's failings were extremely serious and such as to undermine trust and confidence in British financial markets, the BBC reports.
The trader in London had made a number of complex deals which incurred heavy losses.
The British regulator said JP Morgan concealed the extent of those losses.
JP Morgan chief executive Jamie Dimon says the bank has accepted responsibility for its mistakes.