The previous record holder, Fallout 4, did 12 million upon release and over 13.5 million to date, although Bethesda didn't have the return fiasco and probably spent less on marketing and development than CDPR did.
I would imagine that Skyrim sold just as many copies or at least close to that number.
“Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you.”
