How to abbreviate long numbers?

I am designing an interface which has some edge cases where a users balance could be incredibly large, such as 11 digits.

As these are edge cases I don't want to change the UI to account for them. I want to be able to shorten the number, while still allowing people to understand its meaning.

In the same way you may display 1256 as 1.2k how would you display something like 23583578321?