Would riding my bike 6 miles 5 times a week be considered a good cardio workout?

[MSUfan5767]

I ride my bike to work 5 times a week. Each way is about 3 miles, up and down hill. I go at a pretty good pace, and i make it the 3 miles in about 15-20 minutes. At the end of the day when i ride back i try and go faster for a better workout. Is this a good cardio workout? or more of just a basic bike ride? Thanks!