According to this fantastic book called Burn that just came out, which cites a meta-analysis of 23 studies:
kcal/mile = 0.69 × Weight (pounds)
The average adult is 150lbs, hence ~100 kcal/mile as a rule of thumb.
The longer answer: your total daily energy burned is less than you think because your body shifts energy away from resting energy as you burn more in physical activity. See Fig 1 in this paper to see what I mean.
Going on a tangent now, but that's actually a good thing: your body goes nuts when it doesn't get enough exercise and starts wasting energy on things like your stress response (which causes overeating and much more), reproductive system (too much testosterone/estrogen can lead to cancers and other issues), or immune system (inflammation causes asthma, allergies, autoimmune disorders, and a host of other complications).