Updated from 2:18 p.m. ESTThe nation's two biggest banks, Citigroup ( C) and J.P. Morgan Chase ( JPM), say they learned their lesson about fancy financing after being raked over the coals for Enron. But skeptical lawmakers on Capitol Hill aren't so sure. So, a Senate subcommittee will hold an all-day hearing Wednesday to see if the banks really are changing their ways in the aftermath of one of the nation's biggest corporate scandals, and discuss the need for possible stiffer regulation. In advance of the hearing, lawmakers released a new batch of information that paints a highly unflattering picture of several previously undisclosed business deals between the two big banks and Enron. The release of the information and news of the hearing helped drive down shares of Citigroup and J.P. Morgan. In afternoon trading, Citigroup's stock was down $1.40, or 3.7%, to $36.15, while shares of J.P. Morgan dropped 93 cents, or 3.8%, to $23.50. The selloff in both stocks is reminiscent of the way Wall Street reacted this summer, when the Senate Permanent Subcommittee on Investigation held a similar hearing to examine $8 billion in prepaid oil and gas deals involving the banks, Enron, and several offshore shell companies. Lawmakers denounced the oil and gas deals arranged by the banks as "sham transactions" that helped Enron inflate its revenue.