"Hundreds of millions."
Ratusan = some arbitrary number of hundreds juta=1 million. Ratusan juta = some arbitrary number of hundreds times one miliion. This is the same thing as "hundreds of millions" in English. Ratusan jutaan = some arbitrary number of hundreds times some arbitrary number of millions, mathematically equivalent but not carrying quite the same literal meaning
Or to put it another way, an analogy. "Hundreds of cats" in English means hundreds of individual cats, not hundreds of groups of several cats. Indonesian would construct this same idea as literally "hundreds of [one] cat", or ratusan kucing (NOT kucing kucing). Now substitute the word "million" for cat. "Hundreds of millions"=hundreds of ONE million = ratusan juta (NOT ratusan jutaan)