3.4 million, the most I've ever had in my bank. I tend to farm bells as and when I need them so I've never had much in reserve. Too lazy to farm every day now.
Main town mayor has 155,000,000. The rest of my players have 102,500,000.
Divided the bells up for all my towns. I didn't want a billion sitting in one town.
I've been playing since the release and don't use bells that often.