It seems like a few years back, 20 million was a bit like the upper limit for A-list actors. But that is the "pure" salary. The Downey Jr sums you mention include (AFAIR) the additional box-office percentages his agent negotiated.

IMDB includes some examples of salaries on many actors' biography pages, like here for Marion Cotillard: https://www.imdb.com/name/nm0182839/bio

I'd also assume that exact salaries are not necessarily public information, so some of the information out there might be estimates and rumours.

I also don't know how much of the money stated as "salary" in the contract goes to the actor and how large of a cut goes to their agent, their management, their PR people, their lawyer, their dog-walker, etc., etc.