Feb 1984 - Dec 1990: Annual Statistical Digest, various issues, Table 2.
Jan 1991 to date: Federal Reserve Board, H.4.1.
Reserve balances with Federal Reserve Banks are the difference between "total factors supplying reserve funds" and "total factors, other than reserve balances, absorbing reserve funds." This item includes balances at the Federal Reserve of all depository institutions that are used to satisfy reserve requirements and balances held in excess of balance requirements. It excludes reserves held in the form of cash in bank vaults, and excludes service-related deposits
Board of Governors of the Federal Reserve System (US), Liabilities and Capital: Other Factors Draining Reserve Balances: Reserve Balances with Federal Reserve Banks: Week Average [WRESBAL], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/WRESBAL, April 20, 2021.
Release: H.3 Aggregate Reserves of Depository Institutions and the Monetary Base (data not included in press release)
The Board of Governors discontinued the H.3 statistical release on September 17, 2020. For more information, please see the announcement posted on August 20, 2020.
Series is calculated using data from the H.3 release as Total reserve balances maintained (RESBALNSW) less Reserve balance requirements (RESBALREQW).
Effective February 2, 1984, reserve computation and maintenance periods have been changed from weekly to bi-weekly. Series with data prior to February 2, 1984 have different values reported from one week to the next. After February 2, 1984, the value repeats for 2 consecutive weeks.
Please note though that this historical concept of "excess reserves" no longer has the same meaning following phase two of the simplification of reserves administration. https://federalregister.gov/a/2012-8562
Federal Reserve Bank of St. Louis, Excess Reserves of Depository Institutions (DISCONTINUED) [EXCSRESNW], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/EXCSRESNW, April 20, 2021.