Answer: They're largely owned by BlackRock and the Vanguard Group, the two largest asset management firms in the world. Moreover, it turns out these two companies form a secret monopoly that owns just about everything else you can think of too. As reported in the featured video:

"The stock of the world's largest corporations are owned by the same institutional investors. They all own each other. This means that 'competing' brands, like Coke and Pepsi aren't really competitors, at all, since their stock is owned by exactly the same investment companies, investment funds, insurance companies, banks and in some cases, governments.

"The smaller investors are owned by larger investors. Those are owned by even bigger investors. The visible top of this pyramid shows only two companies whose names we have often seen …They are Vanguard and BlackRock.

"The power of these two companies is beyond your imagination. Not only do they own a large part of the stocks of nearly all big companies but also the stocks of the investors in those companies. This gives them a complete monopoly.