[Symbiote]

US Dollars and Euros are the national currency for roughly the same number of people.

340 million people live in a Eurozone country.

320 million people live in the USA, plus there's Ecuador and El Salvador.

(516 million people live within the Single Euro Payments Area, where international bank transfers in Euros must cost no more than a national bank transfer. My employer in Denmark has a Euro-denominated bank account; this is presumably typical for businesses in the non-Euro countries in Europe.)