Not just the query string values, it encrypts the path to the resource (and headers, etc) as well. However, another HNer pointed me to an article on side-channel attacks which is helpful to keep in mind when considering privacy:

https://news.ycombinator.com/item?id=5492338

Consider using Fiddler some time without HTTPS decryption enabled and go roaming around HTTPS sites. You'll see how much information it can extract from the transaction.