The Federal Deposit Insurance Corp. (FDIC) yesterday took initial steps to implement a new asset-based fee structure that will cost the nation’s largest banks more to shore up the deposit insurance system. Under the Dodd-Frank financial overhaul law, the FDIC must base fees on a measure of a bank’s assets. Currently, the FDIC calculates premiums solely on a bank’s domestic deposits. The three largest banks — JPMorgan Chase & Co., Bank of America Corp. and Citigroup Inc. — will collectively pay an estimated $1 billion in additional annual fees under the measure, which goes into effect April 1. The new formula favors smaller banks because they largely rely on deposits to provide money for lending, as opposed to larger banks that have greater access to other sources of funding.