That the Federal Reserve is holding a portfolio of long-term assets on its books is not especially unusual – prior to the onset of the financial crisis, we held about $ billion of Treasury securities with maturities of more than five years. Moreover, we have long been authorized to purchase securities issued by government-sponsored enterprises (GSEs).
However, in the current circumstance, the scale of our intended holdings, and the related expansion of the Fed's liabilities to acquire these assets, is unprecedented. Holding such a large portfolio of long-term assets does expose the Federal Reserve, and thus the taxpayer, to potential losses as short-term interest rates rise.