"The President's budget request, submitted to Congress on May 23, 2017, seeks $677.1 billion in budget authority for national defense-related activities [budget function 050]. Of the national defense total, $667.6 billion is discretionary spending. The remaining $9.6 billion is mandatory spending not provided by annual appropriations acts."
CRS Report for Congress, R44908
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html