Sort of. Rust's Standard Library documentation describes the entire language in perhaps the way you're thinking of

https://doc.rust-lang.org/std/index.html

e.g https://doc.rust-lang.org/std/keyword.as.html explains the 'as' keyword

https://doc.rust-lang.org/std/primitive.i128.html documents the 128-bit signed integer type

Or, maybe you are thinking purely a language document like:

https://doc.rust-lang.org/reference/introduction.html