a million miles away
Noticeably distracted, unfocused, or lost in thought. Of course you don't remember me saying that—you were a million miles away the whole time! Are you even listening to me? You seem a million miles away.
*million miles away
Fig. lost in thought; [of someone] daydreaming and not paying attention. (Only one's mind is far away. *Typically: be ~; look to be ~; seem ~.) He was a million miles away during the entire lecture. Look at her. She is a million miles away, not paying any attention to what she is doing.