Both Steven Drennon, and Tom Au, have provided excellent answers, but I wanted to add to them. The important thing seems to be that the other branches of government likely did not know about what was going on. Perhaps some had suspicions, but nothing to the level of allowing them to execute some sort of check on the activities. The reason for this is that the CIA has extremely broad authority to conduct activities as it sees fit:
The Director of the Central Intelligence Agency shall—
(1) collect intelligence through human sources and by other appropriate means, except that the Director of the Central Intelligence Agency shall have no police, subpoena, or law enforcement powers or internal security functions;
(2) correlate and evaluate intelligence related to the national security and provide appropriate dissemination of such intelligence;
(3) provide overall direction for and coordination of the collection of national intelligence outside the United States through human sources by elements of the intelligence community authorized to undertake such collection and, in coordination with other departments, agencies, or elements of the United States Government which are authorized to undertake such collection, ensure that the most effective use is made of resources and that appropriate account is taken of the risks to the United States and those involved in such collection; and
(4) perform such other functions and duties related to intelligence affecting the national security as the President or the Director of National Intelligence may direct.
The wording of these responsibilities is very vague, and arguably purposefully so. Dealing with intelligence gathering in foreign nations is highly unpredictable, and substantial wiggle room seems to be worked into the package. At least that is what the language related to responsibilities reads like to me. The point is the budget for the CIA is secret, and their day to day activities are largely self-regulated. This is both good, and bad.