The CPA building was home to the Conductor's Protective Association, a union of sorts for railway conductors. Its close proximity to Michigan Central Station made it an ideal location.
The history of this building is pretty hazy; at some point it became a bank and had a teller's booth added to the side, and was later used by the LDS church. Interesting to note is how almost all of the first floor was completely sealed off in it's later years. Tennants would have used the side entrance, giving them access to the second floor and above levels. Scrappers have punched a hole in the wall from which they can access the upper floors.
The building likely closed in 2007/08. When we visited a taxicab driver was sleeping on the top floor, and didn't seem to notice us.