a million miles away

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.
See also: away, mile, million
Farlex Dictionary of Idioms.

*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.
See also: away, mile, million
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • million miles away
  • be miles away
  • space someone out
  • spaced out
  • space off
  • mooner
  • lose the thread
  • occupy (someone or oneself) by (doing something)
  • it escapes (one)
  • lose the drift (of something)
References in classic literature
It swarms with a mean kind of leather-headed mud-colored angels - and your nearest white neighbor is likely to be a million miles away. WHAT A MAN MOSTLY MISSES, IN HEAVEN, IS COMPANY - company of his own sort and color and language.
Captain Stormfields Visit to Heaven
During that time, the (https://www.ibtimes.com/nasa-asteroid-tracker-eyes-giant-golden-asteroid-could-make-all-humans-billionaires-2803286) space rock was only about 0.011084 astronomical units or about a million miles away from the planet's center.
NASA Asteroid Tracker: 85ft NEO To Skim Earth On Friday