From the Document: "The President's FY2020 budget request includes $761.8 billion in budget authority for national defense, a major function of the federal budget that includes funding primarily for Department of Defense (DOD) programs but also for defense-related activities administered by other federal agencies, including the Department of Energy. National defense is one of 20 major functions used by the Office of Management and Budget (OMB) to organize budget data―and the largest in terms of discretionary spending. The national defense budget function (identified by the numerical notation 050) comprises three subfunctions: DOD-Military (051); atomic energy defense activities primarily of the Department of Energy (053); and other defense-related activities (054), such as FBI counterintelligence activities."
CRS Insight, IN11083
Congressional Research Service: https://crsreports.congress.gov/