Charles Taylor, a top OCC official who focuses on capital and regulations, said the majority of the complex banks his agency oversees are implementing "simplification" projects.

"We plan to initiate a project soon to compile data that will assist the industry and other regulators in assessing the impact of these actions," Taylor said in remarks prepared for a conference hosted by the Institute of International Bankers.

Regulators are still grappling with how to deal with the risks that complex, banking giants pose to the financial system, almost six years after the housing market crash brought the largest U.S. banks to their knees.

Congress passed the 2010 Dodd-Frank law to crack down on "too big to fail" banks, or firms that would topple financial markets if they failed. Regulators have since begun to address the possibility that some banks are too big to manage.

The OCC, which supervises the nation's largest banks, in recent months has been pressing firms to examine their organizational structures, identify unnecessary or overlapping businesses, and pare down. It calls this effort "legal entity simplification."

The debate over whether mega banks are unmanageable intensified after the so-called "London whale" situation, in which top officials at JPMorgan Chase were taken by surprise in 2012 when a trader in the firm's London office lost billions of dollars on risky trades.

The OCC bore much of the criticism from lawmakers and pro-financial reform advocates for failing to spot JPMorgan's London problem. Officials have since announced several initiatives aimed at banks' risk management and structure.

The OCC also oversees the other big banks, including Citigroup, Bank of America and Wells Fargo.

Its legal entity simplification program ties into other, ongoing efforts to force banks to examine their businesses and plan for their own hypothetical demise, such as the living wills required by the Dodd-Frank law.

Taylor said selling off or consolidating legal entities also could help firms reduce legal costs, control accounting fees and deal with fewer vendors.

The program has shown some results already, he said. Reviewing legal structures has helped some banks meet tougher expectations that the OCC has put in place for risk management, Taylor said.

(Reporting by Emily Stephenson; Editing by Karey Van Hall and Andrea Ricci)