I asked myself a similar question and found out that there is $350T of net worth world wide, more than $150T is controlled by the 1%. If the total debt is $220T then there is $130T of wealth that is not loaned out yet. The central banks of China, EU and the U.S. are holding a few tens of trillions of dollars of debt and buying more all the time. The U.S. Treasury owes the U.S. Fed a few trillion, that is like not having a debt at all.
U.S. consumer debt, (credit cards, car loans, mortgages) is just over $4T and the U.S. Federal Gov. debt is what $25T.
Banks and investors are the ones holding those loans. They are backed by deposits and physical assets or the full faith and credit of the United States of America.
Funny thing is the loans are often sold to raise money to make more loans. These are often called derivatives. I have read but not really believe but read that there are $1,200T of derivatives floating around.
TEK