Well, it is in the standard Fedora repos, but weitjong hit on the answer. the package name is libstdc++-docs, not libstdc++-doc.
you can install using yum.
yum install libstdc++-docs
You can use yum to search for names if you don't know the exact package name, too..
yum search libstdc++
give you this:
[root@tower20 /]# yum search libstdc++
=========================== N/S Matched: libstdc++ ============================
compat-libstdc++-296.i686 : Compatibility 2.96-RH standard C++ libraries
compat-libstdc++-33.i686 : Compatibility standard C++ libraries
compat-libstdc++-33.x86_64 : Compatibility standard C++ libraries
libstdc++.i686 : GNU Standard C++ Library
libstdc++.x86_64 : GNU Standard C++ Library
libstdc++-devel.i686 : Header files and libraries for C++ development
libstdc++-devel.x86_64 : Header files and libraries for C++ development
libstdc++-docs.x86_64 : Documentation for the GNU standard C++ library
libstdc++-static.i686 : Static libraries for the GNU standard C++ library
libstdc++-static.x86_64 : Static libraries for the GNU standard C++ library
Name and summary matches only, use "search all" for everything.
I do notice something is weird, which could explain it as well. I am on F17, and don't have a F16 or older box handy right now, so could someone check it on there as well?
Look at the package name for libstdc++-docs above in my search results. It shows as a x86_64 arch, which means you won't find it if you have a i686 (32 bit) install (there is no corresponding 1686 package) Doc packages are usually noarch