Is there a document that lists the definitions and uses of all of the built-in Custom Report Dimensions and each of their parameters?

I don't think so. I use the Custom Report Dimensions window, which lists what (I think) you are after.

Yes, that is what I've been using too, but I was hoping there was something a bit more detailed. Thanks!

The latest Advanced Configuration Guide for 7.1b has a new table starting on page 24 that lists all the OOTB custom reports, and for each lists the log file field that is used. For those that use the URI Query log file field, the WT query parameters are listed also, along with whether each parameter is in the Dimension or the Measure. It also details whether Visitor History needs to be turned on, and if so which VH category. Same for GeoTrends. Pretty good table, though I wish the table would discriminate between those WT parameters that are non-negotiable and those that are optional.