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Since we are dealing with such large numbers, this post looks for a simple way to address the question, "how much is a trillion dollars?" The $100 Federal Reserve Note has been issued since 1862. It is the largest denomination currently issued. So let us think about $1T as 10 billion $100 bills.

Each note is about 0.0043 inches thick and weighs about a gram. So a stack big enough to make you a millionaire would be 43 inches tall, about the size of a small child, and would weigh about 22 pounds. And it follows that $1T in hundreds would stack 678 miles into the sky and would weigh 22 million pounds.

Exchange rate movements can have large effects on the measured NIIP. For example, the current account deficit in 2007 was about $730 billion, which means we borrowed around 3/4 of a trillion dollars from foreign countries in 2007 alone. Naturally this causes the NIIP to decline: the world's largest debtor country goes more deeply into debt. However, the dollar depreciated almost 10% during the year, and most US assets held abroad are denominated in foreign currency. The BEA estimates a resulting rise in the dollar value of these assets of almost $440 billion, which it adds to the US NIIP.

The net international investment position (NIIP) of a country is the stock of the net claims of that country vis a vis the rest of the world. Roughly, it is our claims on them minus their claims on us. For the US, the NIIP was very positive at the beginning of the 1980s. This reflected past net saving the US had done vis a vis the rest of the world. According to BEA data, by the end of the 1980s this accumulated saving had not only been exhausted, but the US had gone substantially into debt. The same data suggests the net US debt to the rest of the world is currently about 2.5 trillion dollars.