In Detail Meaning

(idiomatic) Thoroughly; including every detail; with all particulars.

Example:   I do not understand it; would you please explain it to me in detail.‎
1898, Winston Churchill, chapter 5, The Celebrity:
  When this conversation was repeated in detail within the hearing of the young woman in question, and undoubtedly for his benefit, Mr. Trevor threw shame to the winds and scandalized the Misses Brewster then and there by proclaiming his father to have been a country storekeeper.
(Military) By engaging small sections of an enemy army rather than fighting a single pitched battle against the entire enemy force.
  Darius defeated the rebels in detail.