Big client privacy concerns

We are currently working with a company that is connected to a big bank. they are concerned about the privacy of their data and also about the information shared by the users of the assistent. We are wondering how this data is protected, where this data is stored, we have allready searched for the answers but we are wondering if there are any useful documents that we can present to the client to further explain how everything is protected. We are also wondering if openAI has excess to the knowledge base and any other data.