Wealth and GDP are not the same thing. So comparing the two is not going to produce useful results.
The first answer to this question gives some estimates for wealth of various nations in 2010. As you see, the **US owns about $58 trillion** (i.e. the combined wealth of all its citizens and corporations, not just the government). By the same estimate **world wealth is about $200 trillion** , so you will see there is plenty left over for the rest of the world (kind of - the US still owns a huge fraction of world wealth relative to its population).
If you want to compare GDP, US GDP is about $15 trillion out of a world GDP of about $70 trillion (this being nominal GDP, which generally needs to be adjusted in some way to be useful). So still enough left over for the rest of the world.