Bank of America Corp., hit by a credit downgrade last month, has moved derivatives from its Merrill Lynch unit to a subsidiary flush with insured deposits. Derivatives are financial instruments used to hedge risks or for speculation. They're derived from stocks, bonds, loans, currencies and commodities, or linked to specific events such as changes in the weather or interest rates. Keeping such deals separate from FDIC-insured savings has been a cornerstone of U.S. regulation for decades, including last year's Dodd-Frank overhaul of Wall Street regulation. Three years after taxpayers rescued some of the biggest U.S. lenders, regulators are grappling with how to protect FDIC-insured bank accounts from risks generated by investment-banking operations. The concern is that there is always an enormous temptation to dump the losers on the insured institution," said William Black, professor of economics and law at the University of Missouri-Kansas City and a former bank regulator. "We should have fairly tight restrictions on that." Bank of America's holding company -- the parent of both the retail bank and the Merrill Lynch securities unit -- held almost $75 trillion of derivatives at the end of June. That compares with JPMorgan's deposit-taking entity, JPMorgan Chase Bank NA, which contained 99 percent of the New York-based firm's $79 trillion of notional derivatives.