The OED gives:
c. colloq. Used to indicate that some (freq. conventional) metaphorical or hyperbolical expression is to be taken in the strongest admissible sense: ‘virtually, as good as’; (also) ‘completely, utterly, absolutely’.Now one of the most common uses, although often considered irregular in standard English since it reverses the original sense of literally (‘not figuratively or metaphorically’).
The first example of of this usage that it gives is from 1769.
Ours is a living language, isn't it?