Department of Homeland Security 'U.S. Secret Service' Budget Overview (Fiscal Year 2018 Congressional Justification) [open pdf - 2MB]
From the Document: "The U.S. Secret Service carries out a unique, integrated mission of protection and investigations. The Secret Service protects the President, Vice President, former Presidents and their spouses, foreign visiting heads of state and government, and National Special Security Events (NSSEs); safeguards the Nation's financial infrastructure and payment systems to preserve the integrity of the economy; investigates financial, and cybercrimes; and protects the White House Complex, the Vice-President's residence and other designated buildings within the Washington, D.C. area."
U.S. Department of Homeland Security: https://www.dhs.gov/