The document is not in the public domain; by default, only you have the right to copy it, create derivative works, etc. Google's TOS says you grant Google permission to do those things as well, as it can't provide the service without copying, possibly translating, etc. But it doesn't grant ownership or anything resembling ownership. The document remains yours, and you get to control its distribution.
People (to whom you've given access) can view the document, but unless you grant them permission to do something more, that's about all.
The data, though, might not be protected. You can't copyright a fact, and you can't exactly call it a trade secret or the like when you're sharing it publicly. Your particular arrangement of the data is protected, so someone can't copy and paste your table for example, but any facts represented by the table may be used freely.