Biographical note: DuffieDarrell: Darrell Duffie is the Dean Witter Distinguished Professor of Finance at Stanford University's Graduate School of Business. His books include "How Big Banks Fail and What to Do about It" and "Dynamic Asset Pricing Theory" (both Princeton).

Dealer banks--that is, large banks that deal in securities and derivatives, such as J. P. Morgan and Goldman Sachs--are of a size and complexity that sharply distinguish them from typical commercial banks. When they fail, as we saw in the global financial crisis, they pose significant risks to...