The largest U.S. bank, JPMorgan Chase, says it lost nearly $5 billion in bad trades this year, more than double its original estimate.

The Wall Street investment bank said two months ago it estimated that losses originating in its London trading office would total about $2 billion. But in a new earnings statement Friday, the bank said it lost $4.4 billion in the April-to-June period and would also restate its first quarter report to show an additional $459 million loss.

The bank's chairman, Jamie Dimon, said that in recent months it had “significantly reduced” the risk in its trading operations and believes it has “put most of this problem behind us.”

Despite the trading loss, the bank reported a $5 billion second quarter profit. Its corporate value, however, has dropped about 15 percent since the trading loss was first disclosed.