With major tech companies, how detailed of road maps do they have regarding future products?

Such as Google or Apple. With the road maps that they keep a secret, how far out do they usually make their decisions on what to include in products.

Such as, do you think Apple already has a very good idea of what the specs will be of the iPhone that's announced in September of next year or even the following year?

Well no one here actually works there so it would just be guessing.

Apple executives and developers know precisely what they're going to put into the next iPhone. They may not know all the details about HOW they're going to do what they're planning to do just yet, but they know exactly WHAT they're going to do.