Or, must it be "Every man is mortal"? How about "Tree is mortal"?
In another sense, "A detailed description of a man", "A detailed description of man" or "A detailed description of Man"?
Man is a mass noun, therefore it cannot be preceded by an indefinite article. Both man and Man are correct.
Beware that if you say:
You are still targeting all humanity, but in that case, the word man has its usual meaning of a person, because you are targeting every man = every person. Therefore, you cannot write this:
This sentence is grammatically correct, but it is a bit awkward. The indefinite article says that you are giving a description of a man in general, a person, a human being, but you are also trying to give a detailed description. Therefore, such a sentence would only work in biology, when giving a description about human body, for example.
On the other hand:
Sounds a lot better and implies that you are going to describe a concrete person in detail.
Last option you presented,
Both are correct and for the missing article, they imply that you are going to describe whole humanity, which again, in connection with detailed sounds a bit awkward, because it's very difficult to say what is a detailed description of all humans, but the sentences are grammatically correct.
Several people have said that Man in this context is used as a mass noun, but I disagree. Looking at the wikipedia page on mass nouns, the characteristics of mass nouns include:
So... if it's not a mass noun, then what is it? I have to confess I'm not 100% positive of this (and don't have easy access to CGEL to check), but I would say that this a usage similar to using a definite singular to refer to an entire class (The blue whale can grow to up to 30m in length), but turning the noun into a proper noun due to familiarity. This latter explains why, in contrast to that usage, there is no need for a definite article, and also the the common practice of capitalising the first letter. (I guess you could say it is an example of synecdoche.)
Has anyone considered that 'Man' might refer to the species? " The Diplodocus died out; the mammoth [or mammoths] died out; even Man is mortal." Of course this wouldn't be what the reader first thought of, but it is a possibility, and I can't immediately see how to differentiate from the normal meaning, namely One of the characteristics of Man is bipedality; another is mortality.