There are about 275e6 cars in the USA (1), electricity generation is 4171e9 kWh/year (2), double the generation figure and you could have 4171e9/275e6/365.25= 42 kWh/car/day.
(1) https://www.statista.com/statistics/183505/number-of-vehicles-in-the-united-states-since-1990/
(2) https://www.eia.gov/tools/faqs/faq.php?id=427&t=3
I'm not following what you are trying to say here or what your point is.
If all the cars in the USA were EVs, how much more electricity would they need?
Generating 2x as much, they'd have 42 kWh/car/day which is +200 km/car/day (124 miles).
If this is what you're trying to determine, then may I suggest you go this route:
In the US, the average car drives 14,000 miles per year, or about 40 miles per day.
Most EVs get between 3.5 and 4.5 miles per kWh (at least today). I will stipulate that in the future, as bigger and less aerodynamic EVs like SUVs and pickup trucks are made electric, that figure will probably drop. So let's even call it 3 miles/kWh.
That would be 13.33kWh per car per day, not 42kWh/car/day.
So that is the additional energy that must be generated. But something you did not address (but which I see asked about all the time) is this:
13.33kWh/car/day = 4869kWh per car/year
times 275e6 cars in the US = 1339e9 kWh per year for cars
which is 32% more than we are generating today
Does that mean we need 32% more generating capacity in the US?
Definitely not, because most of our generating capacity is sitting idle at times that EVs would be charging.