If anybody is interested in the science-tastic part of this it's basically all to do with how binary numbers work.
Your money is stored in a 32-bit binary number and, because of the way binary works the maximum positive integer it can hold is when all the bits apart from the first one (which is used to indicate if the number is positive or negative) are active. The binary number in question (01111111 11111111 11111111 11111111) has a decimal value of 2147483647.
If all the bits are active (giving you 11111111 11111111 11111111 11111111) then the decimal value of the number will be -2147483647.
Essentially when the first bit becomes active, that large amount of cash you have accumulated becomes a negative. Hypothetically speaking, if you could lose just $1 when you have $-2147483647 you would be back on $2147483647; although I am not sure if or how this would be possible.
Not sure if I have explained it that well but there you have it.
There are 10 types of people in the world. Those who understand binary and those who don't.