Halo:TMCC is the 78th best selling video game item so far and it has not even been released yet (http://www.amazon.com/gp/bestsellers/2014/videogames/ref=zg_bs_tab_t_bsar#4). The Halo game has already surged past Watchdogs' sales indicating that Halo will open with far more than a million first week. Based on trends I believe Halo will put these number:
-2 million first week
-4 million in 2014
-8 million by the end of 2015 lifetime with bundles
-10 million when its done selling completely.
The game is consistently in the top 20 outselling all versions of the new Call of Duty until very recently when Advanced Warfare recieved a launch trailer.
I will update as time goes on!