JPMorgan Chase & Co. Chief Executive Officer Jamie Dimon spent much of his time at a hearing where U.S. senators aimed to put him on the defensive firing back at the federal regulatory system.

During more than two hours before before the Senate Banking Committee, Dimon described a $2 billion loss in the bank's chief investment office as a hedge that "morphed into something I can't justify," and largely blamed subordinates for a trading strategy gone wrong. The bank is looking at clawing back some of the compensation earned by those responsible, he said.

At the same time, Dimon, one of the most vocal bankers in challenging stricter regulation, said it would be hard for federal agencies to decide on a final version of the so-called Volcker rule, which bans proprietary trading for a bank's own account.