This is unfortunately no longer true. The Fed set the required reserve ratio to 0% last March. They still incentivize holding cash reserves by paying interest t

This is unfortunately no longer true. The Fed set the required reserve ratio to 0% last March. They still incentivize holding cash reserves by paying interest to banks roughly equal to what they could get by holding something like commercial paper, effectively giving banks free money since there isn't actually any risk, but they technically no longer require banks to hold any cash at all. Of course, the Fed allows this because demand deposit accounts at banks are insured by the FDIC, so people will get their money back even if the bank doesn't have it.