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

Release: H.3 Aggregate Reserves of Depository Institutions and the Monetary Base  

Units:  Billions of Dollars, Not Seasonally Adjusted

Frequency:  Monthly

This series has been discontinued. As of July 11, 2013 data in the new H.3 statistical release are no longer adjusted for regulatory changes in reserve requirements and are no longer seasonally adjusted. The Federal Reserve Bank of St. Louis publishes adjusted monetary base at https://fred.stlouisfed.org/series/AMBNS.