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

Release: H.6 Money Stock Measures  

Units:  Billions of Dollars, Not Seasonally Adjusted

Frequency:  Monthly

For details, please see http://www.federalreserve.gov/releases/h6/hist/.
On March 23, 2006, the Board of Governors of the Federal Reserve System ceased publication of the M3 monetary aggregate and its components. For more information, please refer to http://www.federalreserve.gov/releases/h6/discm3.htm.