Big banks should be banned from credit trading, says Stiglitz

Did Prof Stiglitz comment on whether trading credit on exchanges would be enough to solve the problems he sees with the exposures at the big banks? I certainly agree those positions are troubling on a number of levels - I have always thought the positions were built more easily in an over the counter system. The light shown on exchange traded positions (I thought) would go a long way towards limiting systemic risk. I'm not sure it makes sense to ban any institution from trading anything but would certainly be in favor of more transparency and the discipline imposed by an exchange.