The bank also reported a significant inflow of customers' assets in its private banking unit, something that surprised analysts.
Its private banking unit added net new investments of about $2.6 billion in the third quarter.
Sony announced its new banking unit in March 2000.
The American banking unit now has about 8,000 employees and assets of about $23 billion.
The decline stemmed largely from a $625 million loss at the company's banking unit.
It is also seeking buyers for its loss-ridden banking units.
The loss of the private banking unit was a particularly severe blow to Citigroup.
But, as a banking unit, that will form part of the screening in the banking area and can be an important protection.
The company's main retail banking unit would remain intact.
At a bank like Citibank, the private banking unit is split into regions and sometimes, where warranted, individual countries.