Create a finite state machine $($FSM$)$ modeling the functions of an ATM. The ATM should initially be in the "Idle" state. If a user inserts their card, the ATM transitions to the "Identity Verification" state. After successful verification, the user may choose to withdraw a certain amount of money. However, if the total amount of money in the ATM is insufficient, it transitions to the "Error" state and cancels the transaction. If there's enough money, the ATM completes the withdrawal process and returns to the "Idle" state. Include a mechanism to check the total amount of money in the ATM and provide a warning to the user if necessary. Draw the FSM diagram and explain the necessary operations for each state.

Note: You may assume a predetermined total amount of money in the ATM and a specific withdrawal amount chosen by the user.