How much privacy is automatically given to the customers of a bank in the US? I understand that Johnny Q. Public can't just walk in off the street and ask for information on a customer, but if a law enforcement agent needed information for an investigation (like addresses, how much money is in the account, who has access to the account, etc.) would they automatically need a warrant?

Are banks ever willing to cooperate and give that information without a warrant (as a good-faith/we support law enforcement/we have nothing to hide thing)?