Disclaimer, I work at Google, but I recommend reading the ToS for Google consumer and business services, and I believe the short version of the policies on this have been documented on the Google blog several times. I can't comment on the policy directly, but encourage you to research it, there's a pretty straightforward answer.

Separately, the industry standard elsewhere appears to be that if you're a free user your data is used for training, and if you're a paying user it's not.