Wall Street firms are readying for a 20 percent drop in profit after the Senate passed a financial reform bill Thursday. Industry critics say that Senate version of the bill is tougher than the House bill passed in December (one analyst called it "miraculous" that this happened.) The bill's biggest impact could be on the derivatives market, which, according to The Wall Street Journal, accounts for half of all trading revenue for major banks. That revenue could be halved under new rules. Wall Street's advocates in Washington say that the requirements will up the cost of borrowing for the banks and push business overseas.