About how much cash do you think Bill Gates really has?

I know his "Net Worth" is around 54 or 57 billion but that is like investments, stocks, property, cars, that all total up to 54 billion. How much "Actual Cash" Do you think he has? Like if he was to go to the bank and withdraw all of his cash how much do you think it would be? I'm gonna guess probably around a 4 or 5 billion.