The U.S. Treasury on their plan to unload $142 Billion (notional) of mortgage backed securities, from the Q&A:
...Why is Treasury winding down its MBS portfolio?(Page 1 of 7page PDF)
Selling MBS is consistent with the general pattern of Treasury divestment of financial assets acquired during 2008 and 2009 as part of the various financial stabilization programs. Aided by such programs, today, the market for agency-guaranteed MBS has notably improved along with broader financial conditions since Treasury acquired the portfolio.
Additionally, Treasury’s mission does not typically include managing a large mortgage portfolio....
HT: Market Talk