Federal Reserve and Balance Sheet

In a normal business, basic laws of economics apply, especially every resource being limited, except for wants. I hear people talk about QE and QT, and other monetary tricks which either "increase or decrease the assets on their balance sheet.

The Fed is different though. My understanding is any money the US government needs to fund its deficits, it borrows sometimes from the private sector, other governments, but largely from the US Federal Reserve. The thing is, that the Fed lends out frequently never existed before. They enjoy the right to print their own resources (ie. like Mandrake from the book "The Creature from Jekyl Island").

How could you have a concept of a balance sheet in the accounting sense if everything could be printed? What entry would you do to say invent a few billion USD?