The Arabic word 'fasala' means 'he separated, divided or put apart (a thing from another thing)'. 'fasl(un)' means 'a separation, division, or partition (between two things)' or 'distinguishing between what is true and what is false'. 'fasl-al-khitaab' means 'distinct or plain speech; which to whom it is addressed plainly or distinctly, understands; which is not confused or dubious; such as decides, or distinguishes between what is right and what is wrong, and what is true and what is false, and what is sound and what is corrupt, what is correct and what is erroneous'. 'tafseel' means 'explaining distinctly'. It does not mean 'giving DETAILS'. 'mufassal' does not mean 'detailed' but it means 'distinct'.
The Quran mentions that it is alkitaba mufassalan. It does not mean that the Quran contains details of everything but it means that it is the book which states everything in it distinctly and clearly. Most of the translators of the Quran have made error in translating the word 'mufassal' as 'detailed' rather than 'distinct and clear'. Muhammad Asad, G. A. Parvez and Shakir Ali are among those who have translated this particular word correctly in their renditions.
Apart from the few of the commandments, the Quran has dispensed with the details of many of the Laws enshrined therein and has only given the principles. The first ever details were decided by the Messenger [p.b.u.h] in consultation with his companions, according to the circumstances of his time. Later on, the successors of the Messenger [p.b.u.h], such as Umar [r.a.] made necessary changes in these details for the changing circumstances during his caliphate, staying within the parameters and principles given in the Quran.
Some of the verses of the Quran about the 'tafseel' and the related words are given as follows [translations are by Muhammad Asad]
[say thou:] "Am I, then, to look unto anyone but God for judgment [as to what is right and wrong], when it is He who has bestowed upon you from on high this divine writ, clearly spelling out the truth?"' And those unto whom We have vouchsafed revelation aforetime know that this one, too, has been bestowed from on high, step by step, by thy Sustainer. Be not, then, among the doubters- [6:114]
for, indeed, We did convey unto them a divine writ which We clearly, and wisely, spelled out - a guidance and a grace unto people who will believe."[7:52]
Now this Qur'an could not possibly have been devised by anyone save God: nay indeed, it confirms the truth of whatever there still remains [of earlier revelations] and clearly spells out the revelation [which comes] -let there be no doubt about it-from the Sustainer of all the worlds. [10:37]
Alif. Lam. Ra. A DIVINE WRIT [is this], with messages that have been made clear in and by themselves, and have been distinctly spelled out as well- [bestowed upon you] out of the grace of One who is wise, all-aware, [11:1]
Indeed, in the stories of these men there is a lesson for those who are endowed with insight.[As for this revelation, it could not possibly be a discourse invented [by man]: nay indeed, it is [a divine writ] confirming the truth of whatever there still remains [of earlier revelations], clearly spelling out everything, and [offering] guidance and grace unto people who will believe. [12:111]
And We have established the night and the day as two symbols; and thereupon We have effaced the symbol of night and set up [in its place] the light-giving symbol of day, so that you might seek to obtain your Sustainer's bounty and be aware of the passing years and of the reckoning [that is bound to come]. For clearly, most clearly, have We spelt out everything!. (kulla shay-in fassalnahutafseelan)" [17:12]
And thus clearly do We spell out Our messages: and [We do it] so that the path of those who are lost in sin might be distinct [from that of the righteous].[6:55]
And He it is who has set up for you the stars so that you might be guided by them in the midst of the deep darkness of land and sea: clearly, indeed, have We spelled out these messages unto people of [innate] knowledge! [6:97]
And He it is who has brought you [all] into being out of one living entity, and [has appointed for each of you] a time-limit [on earth] and a resting place [after death]: clearly, indeed, have We spelled out these messages unto people who can grasp the truth! [6:98]
And undeviating is this thy Sustainer's way. Clearly, indeed, have We spelled out these messages unto people who [are willing to] take them to heart! [6:126]
Say: "Who is there to forbid the beauty which God has brought forth for His creatures, and the good things from among the means of sustenance? "Say: "They are [lawful] in the life of this world unto all who have attained to faith - to be theirs alone on Resurrection Day." Thus clearly do We spell out these messages unto people of [innate] knowledge! [7:32]
And thus clearly do We spell out these messages; and [We do it] so that they [who have sinned] might return [unto Us]." [7:174]
Yet if they repent, and take to prayer, and render the purifying dues, they become your brethren in faith: and clearly do We spell out these messages unto people of [innate] knowledge! [9:11]
The parable of the life of this world is but that of rain which We send down from the sky, and which is absorbed by the plants of the earth whereof men and animals draw nourishment, until -when the earth has assumed its artful adornment and has been embellished, and they who dwell on it believe that they have gained mastery over it -there comes down upon it Our judgment, by night or by day, and We cause it to become [like] a field mown down, as if there had been no yesterday. Thus clearly do We spell out these messages unto people who think! [10:24]
He gives you an example from your own society. Would you agree to make your employees equal partners in the provision We have bestowed upon you? Are you as mindful of them as you are mindful of yourselves? (So do you conceive of a ‘discriminating’ God!) Thus do We explain Our Messages for people who use their intellect. [30:28]
The Quran did not mention the details of everything, however God tell us in the Quran he gave us the details and completeness of our religion through the Quran and Sunna.
5:3 ".....Today have I perfected your religious law for you, and have bestowed upon you the full measure of My blessings, and willed that self-surrender unto Me shall be your religion".
7:158 (Y. Ali) day: "O men! I am sent unto you all, as the messenger of Allah, to Whom belongeth the dominion of the heavens and the earth: there is no god but He: it is He That giveth both life and death. So believe in Allah and His messenger, the Unlettered Prophet, who believeth in Allah and His words: follow him that (so) ye may be guided."
In Quran and Sunna God gave us all what we need to know about religion: God and his attributes, his way of communication with humans, his main prophets and their stories, his angels. Satan, his books, his guidance, his commandments,his laws, his orders, the wisdom of creation, the phenomena related to our creation and the creation of the universe, the day of judgement, the heaven and hell......
Thus the Quran and Sunna contain all matters related to religion inspired to a single man Muhammad (PBUH). The amount of material and knowledge that came to him with no faults or contradiction attested to the inspiration by the creator of heavens and earth.