"Are corporations a materialist or idealist entity?" asks one of my rather confused readers. Neither. Corporations are a matter of law, not philosophy. Allow me to explain.
In physical terms, I could destroy even the mightiest corporations with my bare hands. This is because they are a paper filed in a law-office somewhere. Even the richest and most powerful corporations are just a stack of papers and could be destroyed easily.
But to actually get to that paper, one would have to commit multiple crimes, not limited to breaking and entering, multiple counts of vandalism, and probably assault from the angry humans wishing to prevent this sort of thing. Most of these humans are lawyers, and I'm expecting them to be in a vindictive mood.
A 12th century legal case granted in UK law, and the US law that inherited it, all legal rights and duties of person-hood to corporations when the very slick lawyer attempted to argue that his firm, not being a person, was exempt from the statue in question. The court ruled that his firm was an "artificial person" with all that that entailed, human rights included.
However, unlike human people, corporations can easily be neutralized against any particular agenda. Buy their shares until you control 50% or more of the company, and at the next board election, fire the board, fire the CEO, and replace them with people loyal to you. The corporation now follows your agenda.
Now philosophy wise, corporations are idealist in that everything substancial about them are ideas and legal filings. The physical part of a corporation is a piece of paper on which is printed a charter. It's the abstract legal part that gives them the power that they have.