Department of Homeland Security: Defense/Non-Defense Classification (Fiscal Year 2017 Report to Congress) [open pdf - 302KB]
"This document has been compiled pursuant to language set forth in the Joint Explanatory Statement accompanying the Fiscal Year (FY) 2017 Department of Homeland Security (DHS) Appropriations Act (P.L. 115-31). The report describes the definitions and process used to categorize NPPD [National Protection and Programs Directorate] funding, within the appropriation and program, project, and activity structure as either defense or non-defense."
U.S. Department of Homeland Security: https://www.dhs.gov/