There is a bunch of information on how Google does documentation in the book Software Engineering at Google:

https://www.google.com/books/edition/_/WXTTDwAAQBAJ

One notable practice mentioned in the book is their g3doc system. Documentation is kept in the (google3) repo alongside the things documented. It is encouraged to update the documentation and the code at the same time. This also means the full history of the documentation is available in repo rather than in a separate wiki history.

There is also a system of URL-shortener-esque "go/ links" that allows people to easily link to or jump to documentation. For example, "look at go/foobar". The docs are also exposed in their code search system.