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

The series is calculated by the Federal Reserve Bank of St.Louis.
Prior to 2003-01-01, the data are calculated as excess reserves minus total borrowings plus extended borrowings. From 2003-01-01 till 2007-11-01, the observations reflect excess reserves minus total borrowings plus secondary borrowings. From 2007-12-01, the definition changes to excess reserves minus discount window borrowings plus secondary borrowings. Please, check the latest definition of the discount window borrowings at https://fred.stlouisfed.org/series/DISCBORR.

This series has been discontinued with a phase of the simplification of reserves administration (https://federalregister.gov/a/2012-8562).