There is no single word that describes what you want to describe. It would hardly ever see use. In fact, it's hard to think of a specific example in the real world. Even the largest banks are often willing to lend to individuals. Central Banks, such as the Federal Reserve, meet many of your criteria and they will generally not deal with individuals or with small transactions, so they come close, but they often do not require collateral and their lending function is often secondary to their other functions to the point they are sometimes called "lenders of last resort".
Your initial word of "lender" comes closest. It is broader than what you are looking for, but if used without any attachments, people will default to assuming it is a money lender. You can then explain that this specific lender meets your other criteria of not dealing with individuals, being large, etc. While not limited to them, this term is routinely applied to certain types of hedge funds, the federal reserve, and other entities that do meet most of your criteria in financial and legal documents so it is probably the best word you will find.
With credit to auspicious99 for pointing it out first, "financier" also comes close. However, it would include many others that do not. Merriam-Webster defines financier as:
1: one who specializes in raising and expending public money
2: one who deals with finance and investment on a large scale
A venture capitalist is likely a specific type of financier, especially if they help recruit other early stage investors. But a venture capitalist, at least while acting as such, is more likely to purchase equity than lend money. Also, while it is certainly proper to call a lender a financier, the term is more often applied to middlemen. It would fit the institution you want to describe, but it would also fit a lot of other things.