Source: Board of Governors of the Federal Reserve System (US)  

Release: H.4.1 Factors Affecting Reserve Balances  

Units:  Millions of Dollars, Not Seasonally Adjusted

Frequency:  Weekly, As of Wednesday

Notes:

This series has been discontinued and will no longer be updated. It was a duplicate of the following series, which will continue to be updated: https://fred.stlouisfed.org/series/WSHOMCB

The current face value of mortgage-backed obligations held by Federal Reserve Banks. These securities are guaranteed by Fannie Mae, Freddie Mac, or Ginnie Mae.