The corporate headquarters is not where the bank is chartered.
Ally Bank has an unusual charter in Utah - not Michigan. IIRC the charter is some kind of mining charter. Very few banks have that kind of charter. It has some restraints in its charter as to what they are able to do as a bank.
The former CFO of Bank of America who went to GMAC Financial and Ally was Al de Molina.
BTW Ally has some very good rates.
bkmk