Foreign Ownership of U.S. Debt which in total is 20.24 Trillion.
Foreigners own 6 Trillion of it the majority of the remainder are Americans.
In November 2017, China owned $1.2 trillion of U.S. debt. It's the largest foreign holder of U.S. Treasury securities. The second largest holder is Japan at $1.1 trillion. Both Japan and China want to keep the value of the dollar higher than the value of their currencies. That helps keep their exports affordable for the United States, which helps their economies grow. That's why, despite China's occasional threats to sell its holdings, both countries are happy to be America's biggest foreign bankers. China replaced the United Kingdom as the second largest foreign holder on May 31, 2007. That's when it increased its holdings to $699 billion, outpacing the United Kingdom's $640 billion.
Ireland is third, holding $329 billion. The Cayman Islands is fourth, at $269 billion. The Bureau of International Settlements believes it is a front for sovereign wealth funds and hedge funds whose owners don't want to reveal their positions. So are Luxembourg ($218 billion) and Belgium ($115 billion).
After the Cayman Islands, the next largest holders are Brazil, Switzerland, the UK, Hong Kong, Taiwan, Saudi Arabia, and India. They each hold between $140 and $265 billion. (Sources: "Treasury Bulletin, Monthly Treasury Statement, Table 6. Schedule D-Investments of Federal Government Accounts in Federal Securities, U.S. Department of the Treasury, December 2016. “Treasury Bulletin, Table OFS-2, Ownership of Federal Securities", U.S. Department of the Treasury, December 2016.)