The great unwinding of the Federal Reserve’s massive intervention in the MBS market post-financial crisis is set to begin soon. This week, surprising no one, the U.S. central bank’s Federal Open Market Committee announced it will start to normalize its huge balance sheet next month along the parameters it first outlined in June. From October through December, the decline in the Fed’s securities holdings will be capped at $6 billion per month for Treasuries and $4 billion per month for agency MBS. Next year, the declines will gradually increase to $30 billion a month for Treasuries and $20 billion a month for MBS. Fed Chair Janet Yellen reiterated...