@Zardoz,
The US dollar is the World's main trading currency.
This is mostly down to the petrodollar.
Other countries keep stocks of dollars to strengthen their own currency/economy.
It's natural for the issuers of a global currency to be in debt.
What is of more concern is the movement away from the US to China.
Iran wants payment of the Hormuz toll in Chinese, not American, currency.
If China becomes the global currency America's deficit will become a major US problem.