If you go into the Security Role Setup window and select a specific role, and click Print, it'll give you a report with the tasks that role gives access to and a description of each task, but not all like you're looking for.
The Security Task Setup window report just breaks the tasks down to the operations contained within.
The SY09000 table holds the list of security task IDs, name and description information, you may be able to setup some type of SQL view using that table and any others, to generate the type of report you're looking for.
What's in the SY09000 table is about it as far as what we would have for security task description information.
Thanks