I have been trying to find out information on Michigan banking laws. Generally in Michigan, the law provides that when a bank account is in the name of more than one person, providing for payment to either person or the surviving person, the balance of the money in the accountupon the death of either person belongs to and becomes the property of the survivor.
Any party challenging that the account belongs to the survivor has the burden of proof.
I believe that until a challenge is made, the survivor generally is the owner of the account and would not have to release the bank records.