Feb 1984 - Dec 1990: Annual Statistical Digest, various issues, Table 2.
Jan 1991 to date: Federal Reserve Board, H.4.1.
Service-related deposits are the sum of "required clearing balances" and "adjustments to compensate for float." For more details, see http://www.federalreserve.gov/releases/h41/20120719/
Board of Governors of the Federal Reserve System (US), Service-Related Balances and Adjustments (DISCONTINUED) [WSVCBAL], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/WSVCBAL, May 7, 2021.