I heard the expression ネコでも分かる... mentioned in a TV drama as title for a (fictional) book, in the sense of "...for dummies". A quick search on Amazon brings up a few (real) titles ネコでも分かる... or サルでも分かる...
Is this an idiomatic expression you can use in day-to-day speech, or is this just restricted to these lines of books by particular publishers? If this is a normal speech pattern, are there any other animals commonly employed in this context?
As your hunch says, this expression means "for dummies" in the sort of "explained simply" meaning used principally for instructional materials, much like the line of books in English. It seems predominantly to be used with サル with some mentions of 猫. There are some other kind of punny ones for pandas and dogs and sheep. It doesn't appear to be connected with a particular brand like the "for dummies" line of books, but that's the meaning we can safely assign to it.
In fact, I just checked alc and it says exactly that:
猿でも分かる
for dummies〔直訳すると「ばかな人のための」という意味で、解説書や教材のタイトルなどに使われる表現。例えば、Windows for Dummies（サルでも分かるWindows）、Excel for Dummies（サルでも分かるエクセル）、Oil Painting Set for Dummies（超初心者向け油絵セット）〕
For reference, here is a general google search that shows the different varieties in action.
