This file link contains tables that set forth the interchange reimbursement fees applied on Visa financial transactions completed within the 50 United States and the District of Columbia.
Visa explains that it uses these interchange reimbursement fees as transfer fees between financial institutions to balance and grow the payment system for the benefit of all participants. Furthermore Visa explains that Merchants do not pay interchange reimbursement fees; they pay "merchant discount" to their financial institution. This is an important distinction, because merchants buy a variety of processing services from financial institutions; all of these services may be included in their merchant discount rate, which is typically a percentage rate per transaction.
The document tells us that Visa is not choosing the cost-based interchange fee reasoning but goes for the macro-economic position that interchange reimbursements are required in two-sided markets. It also shows the variety of card-transactions that policymakers and politicians should consider if they speak of card-schemes and card payments.