Quarter Billions of US Dollars 1997-10-01 10 1998-04-01 -5 1998-10-01 -5 2014-04-01 2000 2014-07-01 20 2014-10-01 760 2015-04-01 10 2015-07-01 -20 2015-10-01 -20 2018-01-01 2000