could (do something) with (one's) eyes closed

could (do something) with (one's) eyes closed

Is able to do something with very little or no difficulty, or complete or accomplish something in a relaxed, carefree, or effortless manner. It took me a little while to get used to this job, but now I could do it with my eyes closed! You should ask Johnny for help—he could do this level of math with his eyes closed.
See also: closed, could, eye