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 using data derived from the H.3 and H.4.1. releases.

This series has been discontinued with a phase of the simplification of reserves administration (https://federalregister.gov/a/2012-8562). Contractual clearing balance program was eliminated on July 12, 2012.
Nevertheless, to get at the historical concept of Excess reserves using the new H.3 statistical release, take Total reserve balances maintained less Reserve balance requirements. Alternatively, one can view excess as the amount of balances maintained that satisfy the minimum requirements, which can be calculated by taking Total reserve balances maintained less Bottom of penalty-free band.