I don’t think they had 18 trillion in liability, they just suffered from massive dollar devaluation, hyper inflation.
Zimbabwe couldn’t muster a billion in real assets, let alone hope to guarantee a 100 trillion debt note..
The funny thing about fiat currencies is that they have no intrinsic value of their own so there’s nothing to say that a Zimbabwe dollar is ‘worth’ more or less than ours aside from our collective faith that says a US dollar is worth more than a Zimbabwe dollar.
At the end of the day both currencies are faith-based and are both being inflated into irrelevancy.