How to make a transition animation in Unity?

Question

Unity

I have 3 (essentially 4 animations):

1. Idle
   
2. Idle - Run (Transitional animation to make it smoother)
   
3. Run
   
4. Run - Idle (Like the second but vice versa)
   

How can I set up Animator so that my transitional animations go through once, and then Idle and Run can loop?