These purchases were funded primarily by increasing the stock of reserve balances in the banking system, which compelled changes in the operating framework the Fed uses to achieve interest rate control.4 With an abundant supply of reserve balances, variations in their supply— the mechanism through which the Fed implemented monetary policy before the crisis—would no longer cause meaningful changes in federal funds rates or other money market rates. Implementation of monetary policy therefore required a new operational approach. The Fed’s current policy implementation framework uses a system of rates that it directly administers to influence the level of short-term interest rates, without needing to actively adjust the supply of reserves. Specifically, the Fed uses the rate of interest paid on excess reserves (IOER) held by depository institutions as its primary tool for keeping the federal funds rate in its target range. It supplements this tool by offering overnight reverse repos (ON RRPs) at a specified offering rate to a broad set of counterparties, including eligible money market funds, government-sponsored enterprises, primary dealers, and banks.5 Together, IOER and ON RRPs set a floor on rates, beneath which bank and nonbank financial institutions with access to these facilities should be unwilling to lend funds.6 This framework has been working very well. Since December 16, 2015, when the FOMC began the process of normalizing the stance of monetary policy, it has raised its federal funds target range four times to a current range of 1 to 1¼ percent.
See the Federal Reserve Bank of New York’s report and accompanying data file, “Projections for the SOMA Portfolio and Net Income (July 2017).” 15 These liabilities include Federal Reserve notes (U.S. dollar paper currency), the U.S. Treasury’s General  Account, deposits held by designated financial market utilities and government-sponsored enterprises, and reverse repos conducted with foreign and international account holders. On average, these line items summed to over $ billion in 2017, on top of more than $ trillion in Federal Reserve notes. Fed liabilities are discussed more thoroughly in Lorie Logan, “Implementing Monetary Policy: Perspective from the Open Market Trading Desk,” remarks before the Money Marketeers of New York University, New York City, May 18, 2017. 16 It is worth noting that the size and structure of Fed’s securities portfolio and the role the portfolio played have  undergone substantial shifts at various times over the course of the Fed’s history, reflecting changes in policy implementation imperatives. See Meryam Bukhari et al, “The SOMA Portfolio through Time,” Federal Reserve Bank of New York Liberty Street Economics (blog), August 12, 2013. 17 Throughout this discussion, I focus on forward guidance and use of the central bank’s balance sheet (through  large-scale purchases of additional assets and reinvestment policies, but not funding for lending programs) as possible tools. U.S. policymakers have shown little appetite to pursue negative nominal interest rates, although that is another unconventional tool used by several central banks in recent years.