To calculate the mortality rate for a disease, you divide the number of deaths by the number of infected, not the total population. Dividing the deaths by population unsurprisingly tells you what percent of the total population died of the disease, which is not a rate at all.
During an active pandemic, we don't know whether active cases will recover or die, so in order to calculate mortality rates we have to look at closed cases - for the United States, that means 370,057 recovered, 94,918 dead, a total of 464,975 closed.
94,918 / 464,975 = .204 for an average mortality rate of 20.4%.
This of course is higher than reality because our testing has been concentrated among symptomatic patients in need of hospitalization, but for nations who haven't utterly botched their responses, the average rate for COVID-19 is 6%.