The HNWI and the UHNWI
It seems that the rich don't like being called on it - the word does rhyme with "bitch" after all. But investment banks do track them. One of the joys of Plutocrats is learning the vocabulary - the euphemisms of the day.
A current segmentation is the HNWI (High Net Worth Individuals) and the UHNWI (Ultra High Net Worth Individuals). These respective worthies are defined by their investable funds or (sometimes, alternatively) annual incomes, with typical minima being,respectively, one million dollars and 50 million dollars.
Collectively, they control a very large fraction of the World's total wealth. Credit Suisse counts about 30 million HNWI in the world and about 85,000 UHNWI as of 2011. All these people are rich of course, and the UHNWI are very rich, but you still need to increase your wealth by a factor 20 to make the billionaires club - the peak of the financial pyramid is very sharply pointed.