This needs digging
Institutional investors like BlackRock, Vanguard, State Street, Fidelity, and JP Morgan, now own 80% of all stock in S&P 500 listed companies. The Big Three investors - BlackRock, Vanguard and State Street – alone constitute the largest shareholder in 88% of S&P 500 firms, which roughly correspond to America’s 500 largest corporations. (3). Both BlackRock and Vanguard are among the top five shareholders of almost 70% of America’s largest 2,000 publicly traded corporations. (4).
Blackrock had as of 2016 $6.2 trillion worth of assets under management, Vanguard $5.1 trillion, whereas State Street has dropped to a distant third with only $1 trillion in assets. This compares with a total market capitalization of US stocks according to Russell 3000 of $30 trillion at end of 2017 (From 2016 to 2017, the Big Three has of course also put on assets). Blackrock and Vanguard would then alone own more than one-third of all US publicly listed shares.
http://blogengine.hellevig.net/post/2019/05/13/Extreme-concentration-of-ownership-in-the-United-States-.aspx