Regulation D relates to reserve requirements that are imposed on depository institutions to faciliate implementation of the Federal Reserve System's monetary policy. Sections 204.5 and 204.9 include some recordkeeping requirements for depository institutions falling under this regulation.
Link to the regulation: https://www.ecfr.gov/cgi-bin/text-idx?SID=2240159c84d2d3b48422a5185ff69dea&mc=true&node=pt12.2.204&rgn=div5