Overseas Contingency Operations Funding: Background and Status [Updated September 6, 2019] [open pdf - 2MB]
From the Document: "Congressional interest in Overseas Contingency Operation (OCO) funding has continued as Members debate ways of funding priorities without breaching discretionary spending limits set in law. Since the terrorist attacks of September 11, 2001, Congress has appropriated $2 trillion in discretionary budget authority designated as 'emergency requirements or for Overseas Contingency Operations/Global War on Terrorism' (OCO/GWOT) in support of the broad U.S. government response to the 9/11 attacks and for other related international affairs activities. This figure amounts to 9.5% of total discretionary spending during this period. [...] While there is no overall statutory limit on the amount of emergency or OCO/GWOT spending, both Congress and the President have fundamental roles in determining how much of the spending to provide each fiscal year."
CRS Report for Congress, R44519
Congressional Research Service: https://crsreports.congress.gov/