Courtesy of the FDIC. This is based on June data and the various merged entities (e.g. Wells + Wachovia) are combined. Here are the numbers:
A couple of trillion out of $7 trillion of deposits. You could do the same thing for assets, etc. and get roughly the same thing. Except Citi relies less of deposits as a source of funding.
Prior to the latest round of mergers, the top 3 would be more like 20% then 30%.