Are you sure? You know you can have positive credit on your credit account and negative credit on your savings account? To the bank and the card companies there is no difference. The systems are identical. The difference is only the max negative and max positive that they will allow you to go into.

Further, you own none of it. It is not your money. It is the banks money. When you give your money to a bank, you are handing ownership of it over to them. The bank now owes you money. But your money is gone. You want to keep your money at the bank without handing ownership over, you need a bank safe.