On the usefulness of taxes to curb the leverage of banks' "off-balance sheet" assets.

Summary [The IFRS accounting standards have integrated into the balance sheet of banks most of the derivative financial instruments that we consider here under the term "off-balance sheet", at the price of a certain invisibility of their "leverage effect". We describe the activity of corporate and investment banks and show that these derivative instruments correspond to an intermediation function of risk in the economy where banks do not "carry" this risk on the balance sheet, contrary to the traditional banking business of "transformation". We describe the bank as a source of "increasing the possibilities of market size" that we define beforehand in a general way. Such a source, like any innovation, is synonymous with risk. In this framework, the bank's "off-balance sheet" appears as a leverage effect without natural limits. We then study what could be the taxation systems adapted to three different objectives: correcting and capturing rents, limiting systemic risk, and controlling the "growth of possibilities". A tax base that considers a measure of the absolute value of liabilities associated with derivative positions on banks' balance sheets seems relevant to limit the growth of possibilities and, hence, of risk.