The top 10 percent own 84 percent of stocks [0]. About a third of stocks are owned by various retirement instruments (pensions, IRAs, etc) [1]. These numbers don't add up because it is an apples to oranges comparison, which might not be the breakdown OP was looking for.
0: http://www.nber.org/papers/w24085
1: https://www.taxpolicycenter.org/sites/default/files/alfresco...