regexp_substr help, please

I need to be able to pull just the last name out of a string consisting of 
lastname and firstname, separated by a comma, or space, or comma and
space. 
Complicating matters somewhat is the fact that lastname might be something

like "Mc Kay" or "St. Louis" so simply grabbing everything before the
first 
space isn't sufficient.

The closest I've come so far is
        select regexp_substr ('St. Louis, Ted', '.{4}[A-Z]+') from dual;
but this returns only
        St. L

I thought regular expression matching was supposed to be "greedy", and
take as 
many characters as would satisfy the pattern ("St. Louis" in this case).

What am I doing wrong?