In the USA the next level after one hundred billion is a trillion. We do not use a thousand billion but in countries like England, for the same reason they drive on the wrong side of the road, after a hundred million they go to a thousand billion, hence $1,390 billion is correct. Maybe the author is British.
Well, if the author is British I’m pretty sure it would be written as $1.390 billion. They have opposite uses of commas and periods than we do. Very confusing.
One trillion 1,000,000,000,000 equals 999,999,999,999 + 1. That is 999 billion, 999 million, 999 thousand, 999 plus 1.