How will it be done
The Fed is expected to start reducing the size of its balance sheet by stopping the policy of reinvestment instead of actively selling securities. Ferris and al. project that the balance sheet will fall by roughly $600 billion per year for the first two years, $400 billion in the third year and $300 billion in the fourth year. Eventually, the Fed will hold roughly equal quantities of Treasury debt and MBS.

Confidence Interval Projections of the Federal Reserve Balance Sheet and Income
By: Erin E. Syron Ferris, Soo Jeong Kim, and Bernd Schlusche – Federal Reserve Board
Narayana Kocherlakota advocates deliberate sales based on economic conditions as opposed to stopping reinvestment as a better way to reduce the size of the Fed’s balance sheet.
The Fed Is Making a $2 Trillion Mistake
By: Narayana Kocherlakota – University of Rochester
What should the ultimate size of the balance sheet be?
Bernanke summarizes the research presented at the Kansas City Fed’s 2016 Economic Symposium, on the optimum size of the balance sheet. There are two main arguments for keeping a large balance sheet: a) it could be a tool for enhancing financial stability; and b) it could improve the transmission of monetary policy.
Should the Fed keep its balance sheet large?
By: Ben Bernanke – Brookings
…but a large balance sheet increases the risk of financial losses which could negatively affect the government’s fiscal position. This could make the Fed a victim of politics, argues Sims.
Fiscal Policy, Monetary Policy and Central Bank Independence
Author: Christopher Sims
From: Princeton University