The loan agreement lists the terms under which a loan is given. The bank is the lender, and any borrowing entity--individual, partnership, company--is the borrower. The loan agreement covers many of the same terms and conditions as a promissory note, although it is longer and more complicated.
The subsidiaries remain private. They are private subsidiaries of a public company. Think about it: if a subsidiary went public, that would mean that its shares were being offered to the public, instead of all being owned by the parent company, and so it would no longer be a subsidiary.
Well there is not one owner of Microsoft because it is a public company, but Bill Gates is the majority shareholder as well as Paul Allen. But for precise info, this is what I can remeber from one of my spreadsheets. Microsoft is a public company. This means there are billions of owners. Anyobody with at least $30.00 can buy at least one share and Microsoft will pay him or her $0.44 USD every year forever.