The United States bond market size (as of 2017) shows that the treasury holds 35.16% of the market, while corporate debt holds 21.75% and mortgage related revenue holds 22.60%.
According to the Securities Industry and Financial Markets Association (SIFMA), as of Q1 2017, the U.S. bond market size is (in billions): Treasury 35.16% Corporate Debt 21.75% Mortgage Related 22.60% 
