Release: Treasury Bulletin
The data is presented by the source as Public debt securities: Public issues held by Federal Reserve banks on TABLE OFS-1—Distribution of Federal Securities by Class of Investors and Type of Issues.
Public issues held by the Federal Reserve banks have been revised to include Ginnie Mae and exclude the following Government-Sponsored Enterprises: Federal National Mortgage Association, Federal Home Loan Mortgage Corporation, and the Federal Home Loan Bank System.
U.S. Department of the Treasury. Fiscal Service, Federal Debt Held by Federal Reserve Banks [FDHBFRBN], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/FDHBFRBN, April 26, 2018.