The U.S. Federal Reserve is considering a rule change that could save the country's eight largest banks combined billions of dollars in capital, in a potential long-sought win for the industry, according to four people with knowledge of the matter. At issue is how the central bank calculates an extra layer of capital it imposes on U.S. global systemically important banks (GSIBs), known as the "GSIB surcharge," which it introduced in 2015 to boost their safety and soundness. The Fed is considering updating inputs it uses in the calculation, which it fixed in 2015, to adjust for economic growth and in turn more accurately reflect the size of the banks relative to the global economy, the people said.