Satoshi Nakamoto posted this 13 years ago today:

"Eventually at most only 21 million coins for 6.8 billion people in the world if it really gets huge. But don't worry, there are (...) 8 decimal places internally."

∞ / 2.1 quadrillion

And on Lightning there are even 3 more decimal places, with the unit called "Millisat" facilitating an exchange rate of 1 billion USD per 1 bitcoin for msat/cent parity.