I haven't had a high regard for Volcker so I was surprised to find he proposes a system that I believe is necessary. In short it is have commercial banks which are commercial banks and have investment banks which are investment banks (eg players in markets - capital, stock and derivative markets). Investment banks cannot be commercial banks and vice versa. Your core system, the commercial banks, is dealing in the public's savings and current money and is fully regulated to ensure its stability and to weather any future crises.
My precis went over your head; you will need, first, to read and understand Volckers speech putting his proposal, http://www.ritholtz.com/blog/2009/02/paul-volcker/
oooh, lofty intellectualism... ...I like it. And a $50 word like 'precis,' to boot. I had to look that word up.