Separation of powers refers to the division of a state's government into "branches", each with separate, independent powers and responsibilities, so that the powers of one branch are not in conflict with those of the other branches.[1]
Like the Dept. of Justice, Dept. of State, Dept. of the Interior, the FCC the EPA, etc. etc., both the FBI and the CIA are housed with the executive branch of government, and are both executive branch agencies. The FBI is organized under the Justice Department and answers to the Attorney General, is a law enforcement agency but also an intelligence agency that reports to the Director of National Intelligence, just like the CIA, which is organized under the Office of the Director of National Intelligence. Congress, the legislative branch, has oversight via control of both FBI and CIA budgets, but the point to be gleaned here is that it is not the separation of powers that prevents FBI and CIA from sharing information, but instead, generally speaking, their separate mandates. FBI is a domestic law enforcement and intelligence agency, while CIA is not a law enforcement agency but instead an intelligence gathering agency that does intelligence analysis, and specifically information only regarding foreign countries and their citizens. Unlike the FBI, CIA is prohibited from collecting information regarding "U.S. Persons," which includes U.S. citizens, resident aliens, legal immigrants, and U.S. corporations, regardless of where they are located.
FYI, SoP concerns branches, not agencies:
Like the Dept. of Justice, Dept. of State, Dept. of the Interior, the FCC the EPA, etc. etc., both the FBI and the CIA are housed with the executive branch of government, and are both executive branch agencies. The FBI is organized under the Justice Department and answers to the Attorney General, is a law enforcement agency but also an intelligence agency that reports to the Director of National Intelligence, just like the CIA, which is organized under the Office of the Director of National Intelligence. Congress, the legislative branch, has oversight via control of both FBI and CIA budgets, but the point to be gleaned here is that it is not the separation of powers that prevents FBI and CIA from sharing information, but instead, generally speaking, their separate mandates. FBI is a domestic law enforcement and intelligence agency, while CIA is not a law enforcement agency but instead an intelligence gathering agency that does intelligence analysis, and specifically information only regarding foreign countries and their citizens. Unlike the FBI, CIA is prohibited from collecting information regarding "U.S. Persons," which includes U.S. citizens, resident aliens, legal immigrants, and U.S. corporations, regardless of where they are located.[1] https://en.wikipedia.org/wiki/Separation_of_powers