Institutions own about 78% of the market value of the U.S. broad-market Russell 3000 index, and 80% of the large-cap S&P 500 index. In dollars, that is about $21.7 trillion and $18 trillion, respectively. By comparison, institutions hold about 58% of the companies in the S&P Euro index.
Of the 10 largest U.S. companies, institutions own between 70% and 85.8%. Investment advisers are the largest institutional owner of equities through mutual funds and other investment vehicles. Apple, the largest company by market cap, is the most widely held company by institutions, with Vanguard, BlackRock (BLK) and State Street the largest holders.