If so, I have some very good news--and some not-so-good news. (Some may know that you can find this info also by running the CFC Explorer--more on that in a moment.) The unfortunate news is that it's not yet COMPLETELY documented, but it's still a good start.
What IS documented?
So the good news is that the Admin API is now documented here:
It shows the names of the CFCs and (at least for what's there) each CFC's methods and their arguments, including descriptions. That's sweet. Thanks, to whoever at Adobe put those there!
What is NOT documented
Now the bad news: sadly it currently ONLY documents the first 7 of the 18 AdminAPI CFCs. There are 11 more that it does NOT currently document. I asked, and someone at Adobe said it's a "work in progress" that should be updated over time. (That was some months ago. I didn't want to wait any more to point it out, in case it may help some readers. Also, perhaps this can engender some renewed interest in their completing the work--or perhaps some may want to contribute to the effort.)
Technically, this is a chapter in the CF docs
If you didn't notice from the URL above, technically this is a chapter of the "Configuring and Administering ColdFusion" manual, and actually the last one.
How can one know it's last chapter of that manual? Well, it's not obvious, since the online docs lack good breadcrumbs or any sort of always-present table of contents. But I did find it as the last section in this online version of that manual's table of contents:
I will add that my review of the CF docs show that this was not added in any previous release's version of this manual. It's only in the current online/CF2016 version of the manual.
How can you find all the API methods documented?
While it will be nice when that online documentation is completely updated, in the meantime there are two ways one can find more complete documentation.
First, note that one can find documentation of ANY CFC (and all the AdminAPI CFCs) by way of the built-in "CFC explorer", which has been a part of CF since CF6. Assuming the CFC is in a web-accessible directory, you can point to it naming the CFC in the URL for that folder.
So, since the admin API is indeed found in CF's wwwroot, then assuming you had the built-in web server enabled for your local CF instance at port 8500, the following would let you explore the runtime.cfc in the Admin API:
Note that the server against which you're doing this must have RDS enabled (controlled in the CF Admin on the page Security>RDS), and then you also must know the CF Admin (or RDS) password to run the tool.
Second, there was an effort undertaken back in the CF8 timeframe to document the Admin API here:
The spartan interface may confuse you: the CFCs are listed in a drop-down in the top right corner of the page. Being outdated, it's missing newer CFCs added since then. And also beware that the method names and arguments may not be accurate beyond use with CF8.
All that said, I do commend Adobe for starting to get documentation of the Admin API into the CF docs, for those who may not be able to run the CFC explorer, or who just want to casually browse/read about the Admin API.
Finally, if you want to learn more about USING the Admin API, that's documented here. And see the "related blog entries" shown below, where I've done posts in the past using the Admin API in various ways.