JPMorgan Chase & Co. Chief Executive Officer Jamie Dimon sought to hide escalating trading losses that surpassed $6.2 billion, misled investors and dodged regulators as a "monstrous" derivatives bet deteriorated last year, a Senate probe found.

The largest U.S. bank "mischaracterized high-risk trading as hedging," and withheld key information from its primary regulator, sometimes at Dimon's behest, according to a report yesterday by the Senate Permanent Subcommittee on Investigations. The 301-page document also shows how managers manipulated internal risk models and pressured traders to overvalue their positions in an effort to hide growing losses in a credit derivatives portfolio in London.

"We found a trading operation that piled on risk, ignored limits on risk taking, hid losses, dodged oversight and misinformed the public," Chairman Carl Levin, a Michigan Democrat, told reporters yesterday after his investigators spent nine months combing through 90,000 documents and interviewing current and former executives.