Large Disc Shaped craft seen from aircraft near Ritzville Wa.I work for an airline as a Maintenance Technician. I was flying from Spokane, Washington, to Portland, Oregon, for a week of training. We were flying at an estimated 20,000 ft (ceiling limit for this aircraft is 24,000 ft) in the vicinity of Ritzville Washington. The date of this sighting was June 22nd at approximately 6:30 am. The conditions were mostly clear with high level clouds in the distance. No clouds were visible in the vicinity of the sighting.I had been taking pictures with my iPhone 6 out of the window due to boredom. I had taken four pictures; I reviewed them and decided to delete them. I turned my attention from the window and deleted the four pictures. This action took me approximately 30 seconds in my opinion. I looked back out the window and immediately saw a large gray disc shaped craft. It was hovering, or at least did not appear to me moving, at our aircraft altitude. I took several pictures and a short video. From my vantage point it appeared to be the size of a shoe at arm’s length. The height of the center dome corresponding to the height of the shoe, and the length of the craft of course corresponding to the length of the shoe.The duration of the sighting was approximately 5-6 minutes. It slowly moved to the north east, or it could have been that our aircraft simply flew away from the object which was hovering. I cannot be certain which. It simply dissolved as an object leaving your field of view does as it recedes from sight.I looked about the aircraft to see if anyone else had witnessed the object. No one else seemed to notice so I kept it to myself. As I work for the airline I was flying on, I was reluctant to stick my neck out. If anyone had looked out the window they would have saw it. We were flying in a westerly direction and the object was to the right of use, which would be north.The pictures and videos were taken with an Iphone 6. I will email them to you. The size of the craft in the pictures and video do not adequately represent the size of the object. It was much larger in person.