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

Release: H.4.1 Factors Affecting Reserve Balances  

Units:  Billions of Dollars, Not Seasonally Adjusted

Frequency:  Weekly, Ending Wednesday

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/