Each player is able to move cash at any time between their cash-on-hand and the relative safety of their bank. There is no limit to the amount of cash that can be stored in the bank.
There is a 10% fee for moving cash into the bank. The fee is reduced if you have Charmaine in your Inner Circle. Withdrawals are free. The bank does not pay any interest.
Players with the Hotwire lieutenant are able to steal from another player's bank in Duels and/or Wars.