Vanguard is not a corporation. It is structured as a mutual company; it is owned by funds managed by the company, and is therefore owned by its customers.
Vanguard has many pieces and parts, many of which are, indeed, corporations. It says so on the bottom of its website: "Vanguard funds not held in a brokerage account are held by The Vanguard Group, Inc., and are not protected by SIPC. Brokerage assets are held by Vanguard Brokerage Services, a division of Vanguard Marketing Corporation, member FINRA and SIPC."
Regardless of its legal structure, I meant "megacorp" in the generic sense of "large company."
If you want a guaranteed return you do not buy bonds or stocks. You buy a money market fund like VMMXX. See https://investor.vanguard.com/mutual-funds/profile/performan...