That's the total population of the entire US, not the population of people who would be eligible for the full wage. There are a number of demographic groups who would not be eligible for various reasons, eg children (~74M as of 2010 census). That reduction alone is $3 Trillion.
Beyond that, it looks like wages being roughly half of the GDP matches our current setup fairly well: https://fred.stlouisfed.org/graph/?g=2Xa