It's not so much Word offering theses Symbols, but the individual fonts.
There are some in each normal font file, there are special font files
filled with symbols only (Wingdings, Symbol, etc.), and there are really
large Unicode fonts potentially containing thousands of glyphs.
There is no such list because the characters that are available depend on
which font you select. There are thousands of fonts that display special
characters, and more are posted to the Net every day.