Source: U.S. Bureau of Economic Analysis  

Release: Personal Income and Outlays  

Units:  Billions of Dollars, Seasonally Adjusted Annual Rate

Frequency:  Monthly

BEA Account Code: W823RC
Social security benefits include old-age, survivors, and disability insurance benefits that are distributed from the federal old-age and survivors insurance trust fund and the disability insurance trust fund.
A Guide to the National Income and Product Accounts of the United States (NIPA) - (http://www.bea.gov/national/pdf/nipaguid.pdf)