The first cargo ship on a short run in Norway will be able to operate autonomously sometime in 2020 according to schedule (Lots of info in this thread earlier) A ferry in Finland maybe even earlier.
That will be followed by short sea shipping within EU waters in 5-10 years or so. (China may be earlier, but for coastal trade only)
When will you see the first large commercial vessel in autonomous operation across oceans?
in 10-20 years maybe. (Depending on how fast change in rules and regulations can be accomplished)
If you ask about when you will see it in USA, I’ll go with Steamer’s prediction. (Based on the present political climate and resistance to change in the maritime fraternity)